While I join Julian in disliking Tom Tomorrow's recent bit of libertarian-bashing, I don't agree that the man has been getting worse in the last couple of years. I do think he went downhill for much of the '90s, culminating in some really witless animations for the Nader campaign—but then he snapped back to life after 9/11, with clever efforts like this one. Indeed, I've sometimes joked that the one silver lining to the terrorist attacks has been the revival of Tom Tomorrow's talents. Does he blow it sometimes? Sure, but he makes me laugh at least once a month, which is more than I can say for most strips.
The political cartoon whose appeal completely escapes me is Day by Day, a comic much beloved in the blogosphere. It's basically a really bad imitation of Doonesbury, except it's conservative instead of liberal. That may make it more palatable to right-wing tastes, but it doesn't make it any funnier.
Update: A reader called "Digamma" informs us that Tom Tomorrow's anti-libertarian cartoon isn't so recent after all. It was originally published in July 2000—in other words, just as Tomorrow was troughing.