Since the US Ban, Carbon Poker has probably been the best place to play. Americans can also play on Bovada, although I'm not a big fan of they layout. Bodog is out there, but I really hate it, plus they limit you to only being able to play 4 tables.. plus the layout tilts me big time.
Pokerstars, imo was the best out there. If you are not in USA you can still play PS.
You can't ask what min buyin is... I mean there's so many different games and stakes... what do you play? SNG can be anywhere from $1-$2000. I don't know the cash stakes on the sites I listed above besides PS, but I know PS ran all the way up to a $10,000NL, maybe even higher. Full tilt ran some extremely high stakes with some pots being as high as 1,000,000 dollars.
Also, just to make sure.. if you're just a guy who kind of plays at home with his friends to drink some beers... you're probably going to get eaten alive.