Well, Rubicon for example has 700 sell-side partners [1]... so, very large. PubMatic, I believe, is similar.
Your other options for mixing stuff in with AdSense would be to find some fairly targeted affiliate programs; however, it's tedious and requires quite a bit of upkeep.
Your other options for mixing stuff in with AdSense would be to find some fairly targeted affiliate programs; however, it's tedious and requires quite a bit of upkeep.
[1] http://www.adexchanger.com/platforms/as-ipo-dust-settles-rub...