Have you considered ditching CPC and going for CPA or affiliate products instead? For example Peerfly (CPA) or Clickbank (Affiliates) This may be easier and more profitable for you too!
Some I've tried are BidVertiser, Adbrite and Amazon Affiliate.. though so far I'm more successful with Google Adsense
If you have large traffic, sell to advertisers direct. This is what I do and I charge my the 1000 impressions (CPM).
Google Adsense alternatives : AdBrite Bidvertiser Chitika Infolinks / Intellilinks Pocket Cents Kontera Clicksor Exit Junction Dynamic Oxygen AdBull