I've been looking into this for a while and I've found a few (
http://www.pacificpoker.com and
http://www.pokerroom.com for example) that have Java based games so you can run them in any OS. As far as reputation, I can't really comment too much on either of them. I'm still hesitant about giving my credit card number to off-shore casinos.
Does anyone know of any Linux based poker applications (not necessarily online games) other than kPoker? No offense to anyone who may have written kPoker, but it's really bad.