for the manufacturers I know a descent amount about:
DFI: best overclocking, most features, very stable
more expensive than most
MSI: great overclocking, lots of features, very stable, relatively inexpensive
can't think of anything wrong with them....
Asus: best Intel boards, but "ok" AMD boards, except the A8N32-SLI (which is a good board)
a bit pricey for their better motherboards
ECS: cheap
not so reliable
Gigabyte: descent quality, highly stable
not good overclockers, general architecture is a little slow
EpoX: cheap
not so good quality