I haven't seen any worthwhile 'ladies of TF2' yet, so I thought I'd have a shot at it myself. I'll try and do all the classes, but first... The Heavy. To quote her cousin:"She weighs one hundred fifty kilograms and fires two hundred dollar, custom-tooled cartridges at ten thousand rounds per minute. It costs four hundred thousand dollars to fire this weapon... for twelve seconds."
Expertise ain't cheap.
Looks a little funny, but I'm trying (without much success) to emulate TF2's shaders via my typical Photoshop colouring. Practice'll help, hopefully.
I used G-Mod to get a screenshot and just whack the gun in -- pretty obvious I'm guessing, but I don't imagine I'll make a habit of it; I just happened to have this pic waiting in the eaves for ages, and didn't want to burn up more time hand-drawing 'Sasha'...
edit: Hey, check out alciha's 'Heavy Weapons Girl'! [link]
Going for a more 'serious' angle than me, but jeez, he's got me beat.