Google has launched their hosted ad manager in open beta, as opposed to the invitation only one they’ve been running for some time. Google Admanager is a straightforward approach to ad managing, a lot easier to use than the otherwise excellent OpenX open source software, for instance. I’d reckon that Google Admanager is a bit much for most blogs, especially if you just want to push out some contextual ads, and sell a bunch of 125×125 button ads. If that’s the plan, I’d go with something like Performancing Ads (a Splashpress Media service), or one of the ad managing plugins out there.
However, if you need more power, then Google Admanager is a good choice. It competes with OpenX rather than simple ad managing plugins and scripts, though, so there’s a threshold before you actually get started. The overview isn’t perfect either, but hopefully Google will streamline everything, and make it more accessible.