My group has decided they want to play a full blown TOR campaign. I've read The Hobbit, LOTR, and The Silmarillion (a long time ago). I'm wondering which books would help me the most with lore knowledge about the region on the game map, especially Mirkwood and surrounding regions? I don't remember The Silmarillion well, so it might be worth returning to. I've never read any of Tolkien's other work.

Unfinished Tales can give you some information, as some of the stories contained therein touch the region.

Cheers
Tolwen

I'm doing this right now too.

I'm finding LotR Appendices A and B (usually found in Return of the King) helpful as quick reference.

The Silmarillion won't have much, if any, info about this region and time. (But it is worth a reread in general if it's been a while.)

I use these wikis too, but there are mistakes:

http://lotr.wikia.com/wiki/Main_Page

http://www.glyphweb.com/arda/default.asp

http://tolkiengateway.net/wiki/Main_Page