Ways to monetize social bookmarking sites?

So, I own a SB site, kinda was bored one night and through one up. It actually gets good traffic for being just a month old and already a top 400k site. I'm expecting to be a top 100,000 site by sometime in March with the traffic I get.

Does anyone recommend any ways of monetizing this? Even if it was something small like $1 a day for putting up a image or something.