Trask at Living Dice has posted a directory of GenCon 2010 Exhibitors and Vendors.
From their website:
Gen Con 2010 draws near and once again here my link list of all of the vendors and exhibitors. The list is a bit longer than last year, which bodes well for the size of the convention and overall health of the gaming community. I could not find a few sites, so if you have any information on the missing links, please post a comment and I will update the list.