Well, a few guys from a chat room I frequent got busy on Bungie.net and the icons they have found hidden in files seem to suggest weapons that, as far as we can tell, are going to be in Halo 3.

A few of these babies look like they'll be pretty fearsome when you see them for real in the game...

http://www.bungie.net/forums/posts.aspx?postID=10549718

(Had to type out the URL, hopefully it works)

For those who don't feel like going to the link...

... ZOMG FLAMETHROWER, CHAINGUN, COVENANT CHAIN GUN.

- Newnab (I may be the first one to break this here at Gamespot... Hm.)