As a librarian, every year I get a very nice little printed guide called Reading Group Choices, Selections for Lively Book Discussions. It is well put together and I like their choices. (You may even be able to get a copy from this company for your book group-checkout their website.)
Reading Group Choices is listed as a merchant wholesaler company out of Maryland. However, their Advisory Board members have impressive backgrounds in the book world.
This year they included a little leaflet called: Top Ten Favorite Discussible Books for 2009.
You can view it on their website at:
I'm not selling anything for them, but their website is a wealth of information for bookgroups if you are looking for ideas.