I just went through this for myself again so I figured I would post it here so that people can find it here in a search sometime. Google actually has other ad sizes that they accept that aren’t listed on the customer support pages at all, and there are a number of other sizes they support beyond the standard IAB sizes that most ad networks accept.

The reason this is important is that if you have a winning banner in say, the 300 x 250 size, its worth a shot to take your winning creative and roll it out to every single other size you can, because there might be some auction you win because your competitors have only made the basic sizes and you, awesome person that you are, went the extra mile to make some of the other less common sizes.

These sizes listed below can change at any time, google also at the moment accepts image ads up to 150k which is a lot bigger than most other ad networks, which generally are 40-50k tops in size. If you are doing animation, most of the first tier networks require it to stop after 30 seconds, and have at least a 1 pixel border around the image, so that people have a clue that it is an ad.

Ok onto the sizes, here we go:

Adwords image sizes
Acceptable file formats: .GIF, .JPG, .JPEG, .PNG, .SWF
File size limits: 150 KB or less for all files.
Supported ad sizes:
250 x 250 square
250 x 360
200 x 200 small square
240 x 400
468 x 60 banner ( standard for many ad networks )
728 x 90 leaderboard ( standard for many ad networks )
300 x 250 inline rectangle ( industry standard everywhere )
336 x 280 large rectangle
120 x 600 skyscraper ( standard for many ad networks )
160 x 600 wide skyscraper ( used at a lot of ad networks )
300 x 600 half-page ad
580 x 400
930 x 180
970 x 90 large leaderboard
970 x 250
980 x 120
768 x 1024
300 x 1050

mobile only
320 x 50 mobile leaderboard
320 x 100 large mobile banner
Caveat, two of these sizes I have never tried as yet. If they don’t work I will edit this post, and if anyone has any other sizes I don’t know about, please list them in the comments.
Happy Hunting!!