Ad buying management and aggregation

http://www.invitemedia.com/

http://adbuyer.com/

http://www.openx.org/market

http://www.clickable.com/

AdCamo http://www.adcamo.com/

AdMeld http://www.admeld.com/

LiveRail Junction http://www.liverail.com/junction.php

PubMatic http://www.pubmatic.com/

Rubicon Project http://www.rubiconproject.com/

Smaato http://www.smaato.com/