You should sell BikeForum stuff here. It would help with your monthly server bills.
There's a site I use for work related stuff that doesn't cost anything: cafepress.com.
You can see an example of my work related site here: http://www.cafepress.com/phnsy_cpoa
I think it would be cool to see a graphic like your banner (with the 2 bikers on the right moved closer to the logo) on a T-shirt or coffee mug.
You could even offer a free gift for membership upgrades then.
"Upgrade your membership, remove ads and receive a BikeForums thong!" (or t-shirt...)
Just a thought