I am actually not that of a sheehan fan, his sound isn't my favorite and the stuff he plays, too, but I really like his technique.
Really diggin Jonas Hellborg at the moment, Stanley Clarke is cool, I really dig his upright bass stuff (and the "Thunder" CD with him, Victor Wooten and Marcus Miller is cool, more laid back and not "shreddy").
And this is really cool-Niels Henning Orsted Pedersen and Christian McBride:
and just look at this, Michael Manring with Sean Malone-Michael Manring is a total psycho, fretless 4 string with Drop Tuners on every string and he slaps and taps the living shit out of it...
And Malone alone:
[ame]http://www.youtube.com/watch?v=cHvk7J7V2i8&NR=1[/ame]
And the whole Obscura "Cosmogenesis" album is full of sick shit, Jeroen plays some pretty cool stuff on his 6 string Warwick fretless thumb.
Oh and just to mention him-Erlend Caspersen, plays vor Vile and Spawn of Possession at the moment and played for Deeds of Flesh, Incinerate and like 10.000 other bands.