From http://forum.rpg.net/showthread.php?620970-%28Mongoose%29-D20-OGL-PDF-Price-Drop:
(Mongoose) D20/OGL PDF Price Drop
Mongoose Publishing has permanently dropped the price of all its D20-era/OGL PDFs on DrivethruRPG, meaning there are some real bargains to be had. Even the biggest 256+ page books are a mere $5.99, and most titles are $3-4.99, with some even less than that!
You can see the full range of these titles at http://rpg.drivethrustuff.com/index.php?cPath=161_201
If you want to round out your collection of Mongoose products this is a good opportunity. I see a few here I don’t have.
If you’re looking for ideas for good products, consider the later ones. I can recommend the Classic Play series — Book of the Planes and Book of Immortals are both on my go-to list, and I’ve been meaning to rework some material from Book of Dragons.
I’m not as impressed with the Quintessential series. They were early in the d20 era and are a little shaky. The Encyclopaedia Arcane series is from about the same time and I found that while the implementation was a little weaker than I’d like, the ideas and focus on topics worked well for me. I go back to them when I’m exploring topics and looking for ideas. The Slayers series is from about the same time as well, but I never explored them at all.
The Ultimate series are decent content aggregators (Ultimate Feats has, as you can imagine, lots of feats) but don’t seem to really add much new.
Basically, if it’s more than 128 pages it’s worth a look, and at these prices, why not?
In the meantime, I think I’ll fill a few gaps in my own library.