fgl has released an ad platform.
We don't have a standalone in-game ad platform for HTML5 games, only Flash and native mobile. But we do run in-game ads if you put your game on our HTML5 mobile platform, and integrate our API. You get access to many features, as well as ads. Even if you have a version of your game with someone else's ads in it, I highly suggest also creating a version with FGL's API integrated. We actively distribute and help sell licenses of these games for you. We'll also pay you upfront to implement the API.
EDIT: I don't have the rep to post a link, but you can find my post in this forum that talks about it. It's called "We'll pay you up to $200 to implement our API"