I started off with a 645AF with no lenses, just an adapter to my P6 Zeiss lenses.
I've since picked up a 45mm N which has got me some wonderful shots on Velvia 50 and Efke 25, a 35mm C a few weeks ago that I've yet to try (although i've got an undeveloped test-roll of PanF50 shot on it), and a 45mm AF in the post (so i'll probably sell the MF 45mm when that comes).
I'm constantly on the lookout for an 80/1.9 in my price-range, but I've also wondered what are the 'character' lenses in the M645-range, they all seem to be rather 'consistent' as Matt said. No equivalent of the 50'cron with the 3D or the Helios 85/1.5 with the funky-bokeh, just good solid performers.
Has anyone used either the 200mm or 300mm APO lenses? I'm sure that I'll never afford them (OK, I can afford them right now, I just can't justify them), just wondering if they're actually worth the $1k+ I see them go for...
Best thing about m645 is that you can get an adapter to use Pentacon6 and Pentax 67 lenses, if we count them then my best two lenses on m645 would be my Zeiss 120/2.8 MC Biometar and 180/2.8 MC Sonnar...