~Alexandrine Parakeet~2 Red Lored Amazons~Blue Fronted Amazon~Black capped conure~4 Green Cheeks~4 Parrotlets~2 lineolated parakeets~9 American budgies~9 English budgies~ And lots of babies :)
We used to use soft wood pellets in the cages at the pet store I worked at. They were really nice, when they got wet they just expanded into sawdust. I would love to use them at home but they are kind of expensive compared to the huge roll of white paper I got for free and have been cutting to size.
I think you are referring to a floor and not a cage bottom. I use good old newspaper. Some nice bird rooms have tiles on the floor. I was in one bird room where the owner put in ceramic tile with a drain so it could easily be washed.
I'd be leery of an actual litter just because of it's ability to grow fungus when wet. I'd probably go with just paper as well, but of course some birds are going to tear it up. If you have the funds for a tile floor, that would be awesome, especially with a drain.