NiCad is old school. NiMH is the newer breed, pretty safe all around. RC has been using them for years. You rlocal hobby store should have all sized, from 1/2 "aaa" to 1/3 "aa" to sub "c"
Of course, now we are up to LiPolymer, which is even better yet, but if you overcharge them, they go BOOM in a big way. Not fool proof...yet.