I use AdBrite, the revenue not quite as good as google.
The only downside I have found thus far is I think you have to create a channel (like in adwords) for each website, you can't just slam the code onto a page.
I think this is because people can buy Advertising DIRECTLY for your site, so you can target an individual websites traffic. So you need to have the right code for each site.
I only signed up 2nd August and currently have it on half dozen quite nothing with more than 100uv/500pv a day and its earning a few quid a day so not all bad.
1 Interesting feature is you get Paid twice on a full page ad, you get paid just for showing the fullpage and again if they click on it.
I tried Miva they are too slow to do anything, I got bored waiting after a week for them to approve my urls.