The NYT had an article today pointing out that, while his national spots are all sweetness and light, Obama's been running some pretty tough attack ads against McCain in key states. But I don't think any of those ads are as tough as this one the Obama campaign just put out in Georgia (YouTube embed doesn't seem to be working; you can see the ad here).
The toughest (and maybe even unfair) part of the ad is the implication that there was some sort of quid pro quo between Reed and McCain. Between that and the footage of Abramoff in his black fedora and McCain appearing with Bush, the only punch the Obama campaign pulled here is failing to mention the Keating Five.
P.S. It's also interesting that while the Obama campaign, as that NYT story notes, has typically not unveiled its state-level attack ads to the media before they've run, it did do that with this one. I think the message of this ad isn't intended just for Georgia voters.