As someone else said, the MGM is a good place to play if you want 'fish' both in the low stakes tourneys and cash games.
The Red Rock Hotel (way out off the strip) has some serious 'grinders' at it. Be careful out there.
The Bellagio, which is probably one of the most well known casinos thanks to TV, has decent players at all levels but you can always find someone who has some money and just wants to say they have played at the Bellagio. Take them down.
The Rio has all the WSOP poker tourneys going now but there are usually some sats and cash games going on. I have played there but never at WSOP time.
If you want and old school
poker game go down to the Horseshoe, they have games all day. But again there are 'grinders' down there, so be careful