They'll take away my spamming license if I don't pimp my setting on this thread. The link is in the .sig. It has the advantage of being around 80 pages long and free. Hope you like orcs!
I didn't give very much info about why Birthright would be a good choice.
Birthright is set up so you can run your own country. In some ways, it's a game within a game. It gives rules for running your own country, and they're independent of whichever edition of D&D you're running. It has a lot of good source info, and the world is pretty well developed. It was made for 2nd edition, so the stats for monsters, regents, and other NPC's are in 2nd edition format. You can pick up the original boxed set and other source material at www.hitpointe.com.
I really think it's worth it because it has so much untapped material that would be good for a campaign.
-Jamie