But one plant I can keep is an Aloe Vera. I would have said you can't kill one, but I did last year by leaving it in the car for a few days in freezing temperatures.
I have a few in a pot at the kitchen window so when I burn myself, I can go pull a leaf and squeeze its juice on my wound. When this happens, I am reminded to water the thing. Maybe the only reason why it survives is that fact that I am a clutz and I need it every so often.
It also has tons of other uses: laxative, sunburns, insect bites, etc.
See TipNut (great website by the way) for how to use an aloe vera plant and all the uses it is good for. And how to take care of it, but since I am actually capable of keeping one around, they aren't too picky.