...One of the coolest ones is Knoppix...
This was my first Linux experience years ago - loved it! Klaus Knopper was an Amiga user, he still pays homage to the Amiga's Startup-Sequence while booting Knoppix. It also moves easily with a script to a bootable thumb drive and is very usable from there (Great way to bypass Windows spyware

). My only bitch: It should be simple to turn OFF Compiz Fusion. It isn't. Better yet, I wish it weren't included.
One of the cleanest and most intuitive distros I've tried is Debian 6 (uses classic Gnome2).