I would recommend purchasing either an ASUS or Gigabyte board. Check out
www.newegg.com for some great deals. Make sure that whatever board you get, it is compliant with your current configuration (IE CPU Socket, memory speed/type/quantity of slots, expansion slots for video cards/network adapters/modems/etc, as well as the size ie ATX/microATX)
If you don't know any of this, I would take my computer in to a local shop and have them do it, however there will be a steeper price than on newegg.