I've discovered that there's an enormous number of garage comps out there, but that's all the more for me to explore. I'm a little wary of dropping big bucks some of the rarer releases (although the aforementioned Pebbles re-release is surprisingly affordable), if only because there's so much else available. I did manage to find a used copy of Back from the Grave vol. 4 (already have vol. 1), and it's excellent as promised!
I also picked up several Norton LP's recently. Norton rules and their prices are great -- $10 for most of their LP releases.
Friday at the Hideout: Boss Detroit Garage 64-67
Aliens, Psychos and Wild Things: Rare & Unissued Virginia Garage 64-67
Both of these are outstanding. I also got all five volumes of Norton's "Unissued Sixties Garage Acetates" series. The quality of the tunes on these can be hit-and-miss, but there's still some amazing gems.
All vinyl so far...I plan to look into CD releases soon -- possibly the Nuggets set, Acid Dreams, or the stuff available at Arf Arf or Sundazed, as suggested.