You can sort of sneak in Deus Ex, at least the first one, not sure about the second one as I haven't played it much.
Alpha Protocol can be played as a bit of a stealth game. I try to play it without firing a round in each level.
Batman: Arkham Asylum is kind of a stealth game in parts, also. The enemies with guns tear you apart in a straight fight, so you have to sneak around them and take them down silently without their friends seeing/hearing you.
Assassin's Creed is fairly stealth-oriented.
Pretty much any Bond/007 game is a
little stealthy.
The Manhunt games are stealthy also.
The Tenchu series is also stealth-based, but I've never played it so I'm not sure if they're any good. It's had 5+ games in the series, so I'd assume it's at least decent.