3rd party definition and suggestions

[Uncle Pine]

Well, I know that the "3rd party" category includes a lot of books with extra stuff (be it classes, rules, templates, etc.). Usually, if it doesn't have a brown cover (or grey cover for FR and Eberron) it's 3rd party. Also, if you have never heard of it and you are not new to D&D, it's 3rd party.
However, how you determine exactly wheter a book is 3rd party or not?

I'd also like to know if there are some 3rd party books that you find particularly useful/interesting/balanced/broken. I play and DM in 3.5e.

[Yora]

If it's anything not made by the creators of the game (WotC or Paizo) or by the consumer who buys their game, but made by someone else.

For Pathfinder I like Psionics Unleashed and Secrets of the Oracle.

For D&D 3rd Ed., the Midnight Campaign Setting is really great.

Conan d20 is also great, but that's more like a different game like Pathfinder.

[Uncle Pine]

Anyone else?

[CRtwenty]

The Book of Erotic Fantasy is one of the stupidest 3rd party books I've ever seen. Had a player bring it over because she thought it was funny. I failed to see most of the humor. The entire thing read like it was written by a 15 year old (Power Word: Disrobe... really?) and I spent more time feeling sorry for the poor models they hired to pose for the pictures then actually paying attention to the text.

I'll admit that their variation on "Summon Mount" cracked me up a bit though.