The GDN can be a great source of traffic if you use it correctly. Lots of our Google Pay Per Click clients initially only use Google Search but when we test the Google Display Network they can be amazed by the results.
Google updates the image sizes possibly for Ads on the GDN frequently so to help you keep up to date we decided to put it all on one easy to understand page. We will keep it updated to ensure it is always accurate. If not please do feel free to let us know.