Don't worry about DDR3. Moving from DDR2 to DDR3 isn't much of an upgrade, and never will be without changing platforms.
Rather than throwing out an arbitrary price range, why don't you define what you need in a board? You've already ruled out SLi, which I assume also rules out Crossfire. How many SATA ports do you need? Onboard RAID? Firewire? eSATA? Overclocking features?