Movies:
28 Weeks Later - Cute Woman with tie on surgical mask

The Abyss - scenes in which an actress wears an SCBA to fight a fire, and tries to get air from a half-mask

After the Sunset - Salma Hayek is in it, but the scenes are kinda dark

Anaconda 3 - cute scientist in a tank top wears a full face respirator to enter a lab saturated with knockout gas.

Batman (1989) - Kim Basinger holds a small mask over her face while the Joker's gas knocks out everyone in the museum around her

Blue Smoke - Lots of up close scenes of a cute redhead wearing respirator.

Cliffhanger - multiple shots of the female villain wearing a full face oxygen mask while she pilots a depressurized airplane during a mid air heist. A silly movie that has a few great action scenes, probably the best of which is the aforementioned heist.

Close Encounters of the Third Kind - a woman puts on an old double-filter US Navy style gas mask just in case the government's report of a toxic spill isn't just a cover up for the UFO landing.

The Dentist - Lots of mask scenes

Down The Drain - ?

Dracula 3000 - woman wears a gas mask adjusted by the props department to be some sort of futuristic oxygen mask.

Final Decent - Drop down airline oxygen masks

Getting Even - well known fantastic scene of a woman gassed while wearing a mask. Long.

Ghost - brief scene of Demi Moore wearing a light duty dust mask at the very beginning. she rather moronically removes it while dust is literally pouring down on her head.

Hostile Force\The Heist - Woman with Police uniform on running around with respirator on. This is one my favorite scenes.

I Know Who Killed Me - A Crappy Lindsey Lohan movie, But has a good scene with a woman wearing a perfectly fit ear loop mask.

InnerSpace - brief, brief scene in which a villainous lady leads a team of men in hard hats, gas masks, and tyvek suits on a sleeping gas spree around a science lab. the unmasking is really strange. A few seconds of her wearing her gas mask, then a quick edit as its removed so her totally 80s hair is fully revealed.

Jerico Fever - Dust Masks

Just My Luck - Lindsey Lohan Movie. But this time she is wearing the respirator and a gas mask

Maid to Order - brief scene of Ally Sheedy cleaning a toilet wearing a half mask respirator.

Mission Impossible 2 - It's such a small scene you have to pause to see it. But it's worth it. you can get a few good screen caps

New Jack City - Women Topless with tie on surgical masks.

Novacaine - 1 Decent scene of a hygienist Removing the mask after wearing it.

One Night at McCool's - Sexy shots of Liv Tyler cleaning a house wearing a half-mask respirator.

Outbreak - Hazmat Suits, Gas Masks,

Real Genius - Decent scenes of the female lead wearing a gas mask while she and her buddies install a tiny radio receiver in some guy's teeth as a prank. They put sleeping gas under his door first.

The Real McCoy - quick but sexy scene of Kim Basinger as a cat burglar donning a full face respirator and rolling a gas grenade across a bank lobby.

Repo! The Genetic Opera - Surgical Masks, Gas Masks, & Futuristic Visors

Roma - Federico Fellini wanders around rome and films whatever he likes for two hours. more interesting than it sounds, and it has scenes where a woman enters an archaeological excavation of some sort beneath the city and wears a dust mask. the scene is fairly long. not bad for 1974.

Shaft (2000) Brief scene of topless women sorting drugs while wearing blue dust masks.

Teenage Caveman - Hot Blonde wearing old-school nuisance mask.

Terminator 2 - brief scene in which Linda Hamilton places an SCBA mask over her face to avoid tear gas. Slightly better scene where she enters a room where a halon system has just gone off.

Them! - a classic sci fi movie that you should see anyway. has a scene where a female scientist dons a 50s style MSA gas mask to enter a giant ant nest after poison gas has been dropped down into it.

What's Up, Tiger Lily - Extensive scenes of an actress getting a gas mask on just in time to avoid a nasty death by fumigation. quite a funny movie in general. Whiffs - Gas Masks

X-Files the Movie - Gillian Anderson wears a dust mask

Yana's Friends - ?

TV Shows:

Alias - (Multiple Episodes)
"The Abduction" Jennifer Garner dons an MSA full face respirator and swings down into a van that has been filled with tear gas. nice donning scene and god shots of her inside the van.

"Doppleganger" Jennifer Garner, looking good in a miniskirt and leather jacket, dons a full face respirator to find and extract a scientist from a building where her cohorts have released invisible knockout gas

The Amazing Race (13- "Please Hold While I Singe My Skull") lots of great scenes of women wearing respirators during a challenge requiring them to spray paint.

The A-Team - ("Say it With Bullets") a female army officer dons a gas mask to escape a cloud of tear gas.

The Avengers - ("The Gilded Cage") - honor blackman infiltrates a gang of thieves that use sleeping gas to knock vault guards out. interesting scenes, because the gang takes her need to wear a mask very seriously, no laughing it off. she also unmasks to talk on the phone, then puts it back on immediately when done.

Babylon 5 - (Multiple Episodes)
bab 5, unlike most sci fi tv shows, paid more than lip service to the dangers of alien atmospheres and oxygen starvation. on hulu.com, you can find the following:

"A Voice in the Wilderness, Part 1" - around the 33 minute mark
"And Now for a Word" - around the 18 minute mark
"Divided Loyalties" - around the 41 minute mark

Batman - ("The Puzzles Are Coming") the puzzler and his gang paralyze a bunch of people with gas. one woman wears a half-mask sort of deal.

Batman: The Animated Series - ("Joker's Favor") Harley Quinn, disguised as a police officer, gases a dinner given in commissioner Gordon's honor. this scene had great potential but Harley is only seen wearing her protective half mask for a second or two. blink and you miss it

Baywatch - ("Hot Stuff") the baywatch babes don survivair full face masks to evacuate the victims of a wildfire that has created a toxic chemical smoke.

Bones - ("The Graft In the Girl") Emily Deschanel rocks a gray valved Moldex dust mask.

The Champions - (Episode 13 - "Twelve Hours) - Sharon Mcready performs surgery

Dr. Who - (Mutliple Episodes)
"Terror of the Vervoids" mel and the doctor wear half masks to enter a room where someone has been subjected to a biological experiment. a fairly nice sequence.

"The Poison Sky" completely moronic episode partially saved by brief glimpses of Martha Jones in a gas mask. one of those idiotic shows where people are surrounded by poison gas, and protective masks are the absolute last thing they think of to help themselves.

Fastlane - ("Iced") incredibly long scene where a female thief dons a gas mask, puts knockout gas into a bank ventilation system, and then works inside the vault. so good you'll forgive the director for only putting a riot control cartridge on her otherwise excellent mask.

Fringe - (Multple Episodes) - Surgical Masks, Gas Masks, Hazmat Suits, SCBA

It's Your Move - ("The Christmas Show") this obscure 1984-85 sitcom had a brief scene where a teenage girl wears a white dust mask to protect herself from the smell of a homemade vat of chemicals.

Jag - (Boot) women gassed in a gas chamber, lots of gas mask action

Jake 2.0 - ("The Spy Who Really Liked Me") cute blonde spy dons a 3m full face respirator to save herself from poison gas.

La Femme Nikita - ("Love") I'm really only putting it here to warn you away. one of the more ridiculous misuses of respirators in TV history. many people run around avoiding 'nerve gas' by wearing survivair respirators without nose cups, bottom straps, or filters. also, the gassing scenes are pretty gruesome and not much fun.

Lost - ("The Other Woman") - brief scene of Charlotte in a 3m full face respirator and tyvek suit, and also looking hot and bothered after removing her mask.

Nash Bridges - (Danger Zone) good one. Lots of scba+hazmat.

One West Waikiki - ("Terminal Island") nurses wear hazmat suits and SCBAs. Lots of close-ups of masked faces.

Red Cap - (Cover story) excellent shots of a girl gassed while wearing a gas mask.

The Sarah Connor Chronicles - (Alpine Fields) totally hot british babe wears a gas mask while exploring a tunnel full of biological weapon victims.

Stargate SG-1 - (Multiple Episodes)
stargate had a number of episodes where samantha carter intelligently (or not so intelligently, in scenes where stuff like protective gloves are left out) wore masks to protect herself against assorted hazards. as the series went on these scenes became less frequent but some of the best are in the following episodes:

"Bane" (m40 gas mask)
"The Light" (3m full face respirator)
"Cold Lazarus" (m40 gas mask)
"Singularity" (m40 gas mask)
"Watergate" (m40 gas mask, also Marina Sirtis in Israeli gas mask)
"One False Step" (rare scene of Janet in MOPP gear and mask)

War of the Worlds - (The Obelisk) season two finale featured a brief scene of suzanne mcculloch in a black half mask respirator.

Will & Grace - (Girls, Interrupted) excellent scene where grace wears a Moldex valved mask while spraying bug spray in a hallway.

Zoey 101 - (Zoey's Tutor) girl genius Quinn wears a half-mask respirator to fill her dorm room with an experimental knockout gas of her own making. when her roommate enters, quinn quickly orders her to don a mask, too.

 Thanks to the following users for their contributions to our list:
bumblebeeman55, dave_isit2010, dominic, F.P.J. Mask, kergan2, Maskman 77, meded112,