Jens! is a great guy, down to earth and a real laugh - great guy to spend a night in a bar with. Tony Martin is also a genuinely nice person. Kittel too. Boonen is very friendly and approachable, but from what I've heard I wouldn't want to go drinking with him - no way I'd keep up! If you're younger though..... Keisse is a nice guy, calls it as he sees it, but very open. Vanmarcke is friendly too. Greipel is total sweetie.
Cadel used to come across as grumpy, but away from a race he's really one of the nicest people you could hope to meet anywhere. He seems to be more relaxed and to be enjoying himself around races too now, which is nice.
I was lucky enough to meet Contador one day (in a completely non cycling situation, completely by chance - I was with a Spanish friend who knows his family well). He's great. Modest, unassuming, genuinely interested in other people - and offered to buy the drinks immediately!
On the whole, both from experience and what I hear from others, I think that the majority of pro cyclists are at least OK people. It probably is easier to name the ones who aren't.
Oh, and I know this is an unpopular opinion amongst (some) cycling fans, but David Millar is a great guy - great sense of humour (often against himself) and very down to earth.