Ha, I can make this wish come true. Right about now. Look for it in about 15 Minutes on: www.systemreferencedocuments.org (right, that's where all the cool kids look for the SRD stuff)
The Wizards Amulet, by Necromancer Games. Not only did it help me figure out the 3.X mechanics, but it also was a fairly interesting adventure, and led nicely into The Crucible of Freya, which knocked my player's socks off.
I'd also have to cast a vote for Northern Journey as well. The fact that these guys don't charge for so much work is astonishing.
1) The FanCC provides numerous netbooks, some of which are excellent, while all are free. Here is a list of some of them: Netbook of Witches ; Netbook of classes ; Netbook of Races ; Netbook of Feats ; Netbook of Time (i.e.: Chronomancy) ; Netbook of books (by myself!) ; plus (on the "Miscellaneous Netbooks" page) Netbook of Chocolate ; Book of Beasts vol 4 ; and Diadamon (a whole pantheon extremely well done and detailed).
2) Michael Tresca has created numerous excellent sci-fi supplements for d20 Modern (Alien, Terminator, Predator, and Matrix). They are certainly worth checking!
3) The free Amethyst d20 campaign setting (260 pages), which is the free setting I prefer above all the others. See the link in my signature.