Looking at one of the latest Bundles of Holding, I am quite impressed by the quality works included at these price points. Truth be told, I believe I already own everything, if not in print than in PDF. That says a lot IMHO.
With the Goodman Gems bundle, you get The Adventurer's Almanac, the DM Campaign Tracker, PC Pearls, and GM Gems for 9.99. If you increase your buy-in to about 26 bucks, you also get The Dungeon Alphabet, The Monster Alphabet, The Cthulhu Alphabet, 50 Fantastic Functions for the D50, and How to Write Adventure Modules that Don't Suck.
It's a pretty damn strong collection overall.