Have any libraries tried using Meetup.com to advertise library events?  It seems like a good platform for outreach, I've used it personally to find local groups, including book clubs.  They seem to have non-profit pricing as well, though I'm waiting to hear back on exactly how generous that is; the $35/month groups are normally charged isn't unreasonable anyway.  Definitely interested in hearing if using it has proven a success (or failure) for anyone.

Don Priest
Southgate Veterans Memorial Library
14680 Dix-Toledo Rd.
Southgate, MI 48195
734-258-3002 ext. 3003