There is some question as to their legality and some have poor reputations for paying out. I also know only USA players are allowed on some of these sites. And with the reputation of the USA authorities it's not impossible that their funds may suddenly be seized and the sites closed down! USA-based players play on these sites because they have no option. My heart goes out to them - The Land Of the Free indeed!
If you are in some European countries you will still have limited options - Spain,
france and Italy I know allow only the sites which are licensed there, and these are mainly the big boys like Pokerstars, Bwin and
888.
If you have other options, Google I-poker and look at their skins (the sites that use their software) or try microgaming.
PokerOrifice on Nov 27th gave a good all-round list of sites - any of them should be OK. Not sure what you meant by 'good' sites.What's the matter with PokerStars?