I had lice when I was in kindergarten. We used Rid:
http://www.ridlice.com/index.html
I think it's the major lice/nit shampoo.
The important thing is no matter what you have to make sure you're treating/removing the nits as well the live lice.
The other important thing is to bag up stuffed animals and things like that for several months.
I say this, but I seem to remember hearing or reading somewhere that lice are becoming increasingly resistant to lice shampoos... eek!