I'd be wary of the Hitman games if looking for stealth, personally. On one hand, the disguises, gadgets and open level design are cool, but there's a painful lack of the ability to hide in shadows, and the AI of those games can be great one moment and completely inconsistent and ridiculous the next. I'd have to say out of all the stealth-oriented games I've played, that series has given me the most headaches.
They're a very different kind of stealth games, that's for sure. Any hiding based on line of sight or shadows is not really reliable. It's mostly about hiding in plain sight with disguises.
Still, I think Hitman Blood Money pulled it off really well.
Chronicles of Riddike: Escape From Butcher Bay
Yes, very nice.
Stealth works pretty well in Vampire: The Masquerade - Bloodlines. And games like Amnesia: The Dark Descent and the Penumbra series are horror games with a stealth element to them.
And keep an eye on Dishonored which is being published by Bethesda. If it lives up to its promises it's going to be fantastic.

I don't own any Splinter Cell game but they sound interesting. Which one is considered the best?