jpch - 4:43 pm on Oct 7, 2011 (gmt 0)
I've been using Lijit for about six weeks after my other CPM netwrok started having issues. I've found them to very easy to work with, responsive to emails, and pay a decent CPM for my site. They did contact me first via email after finding my site on a search. If you read up on them you'll see they are geared towards the smaller publisher...the one's Federated never would have touched or many other ad networks.
One note - CPM for foreign ads is very low so if you have a lot of visitors outside of United States they might not be a good fit for you.