I vote for a sim that has a wheelchair. I used to have one for TS1 and honestly, it was strange to watch that thing go down stairs and use the toilet. The wheelchair stayed with him so it looked like he was just rolling the chair over the toilet and down the stairs but it caused no other real problems.
Honestly, I am surprised that Maxis hasnt released a package or EP similar to the holiday pack with add ons for handicapped Sims and accessible community lots etc. I think that would make the game more realistic. Also, they include a UFO crash in their game for the neighborhood screen so why not have some strange defects caused from radiation which will render a sim handicapped in some form or another? Makes sense. I know im not the only person who requested this kind of thing with TS1 and I had a really hard time finding the wheelchair sim that I originally had. When my computer crashed I lost him and havent been able to find him since.
Please create one if you're thinking about it and let me know.
I found this image of a wheelchair sim that someone was working on from a while back, looked like they may have been working on it in a 3D program and maybe for TS2.
I think there are a lot of possibilities for handicapped sims in the game. For instances, if there's a sim that's totally disabled, assign that sim a care-giver and enable other options for feeding, etc for the caregiver and make that a career in the medicine field or something. Make certain things such as stairs inaccessible to sims in wheelchairs to make it more realistic but have sims that are also handicapped to a lesser extent and therefore they have access to more functions in the game without the assistance of a care-giver.
__EDIT__
I just found that link for TS1 wheelchair sims at
http://madeforsims.planetthesims.gamespy.com/Skins___Faces/Misc_Skins/misc_skins.html