FreeDirectMedia - 6:25 am on Feb 26, 2012 (gmt 0)
It depends on what kind of ads you are looking to run.
30,000 monthly uniques is enough traffic to get your site approved into some top tier CPM and Affiliate Networks.
I suggest looking in Burst Direct, RMX, and ValueClick Media for CPM placements.
Look into ValueClick, W4, and Clickbooth for affiliate offers.