rg01 :
Will a GeForce GTX 580 graphics card fit on a Micro-ATX mobo?
Yes, a GTX580 will fit in any Micro-ATX or even mini-ITX motherboard that has a x16 pci-e slot, and every one I can think of qualifies.
You will be restricted in your choice of M-ATX cases that can handle a card of that length(10.5").
The Silverstone TJ08B-E will hold one, and is one of the best.
Lian li also has some, but cpu cooler sizes are restricted.