Of the one's I've met/spoken to for more than 30 seconds:
1. Jonas of course :P
2. Alexander Popp
3. Simon Aspelin (debateable. He could also share first place with Jonas)
4. Wayne Ferreira!(retired), Niclas Larsson (wheelchair), or Brian Vahaly
5. Alex Bogomolov Jr / Filippo Volandri / PimPim
Other mentionable guys that have been polite & friendly:
Oli Rochus, Max Mirnyi (and his dad!), Todd Martin and Mats Wilander!
If I left anyone out, I prob haven't paid much attention to them.