Chris Bowen created a create blog post about publishers offering support for user groups. It is a great post that you should all be aware of. 
It lists many publishers and links to the programs they have setup for user groups. ie, how to get free books for your group meetings!!!!
In addition to his list, you should also be aware of MS Press books which are available through UGSS at http://www.ugss.codezone.com
User Groups, community, Dan Stolts