Barack Obama's campaign has ads on the Margolis boys' HubPolitics and DevalPatrickWatch blogs.
Although the names might suggest these are good sites to go trolling for potential Obama supporters, in fact they are rabid right-wing liberal-bashing sites, as the briefest of glimpses would reveal.
Plus, as far as I've ever known, this is the first time anyone has placed an ad on either site (not counting ads for their own sites or those ubiquitous little google ads).