I'm just wondering if any of you know of an ad network that provides ads in custom dimensions chosen by the publisher. AdSense and other popular networks have a bunch of ads with pre-defined sizes, but none of them suit my design. Before I'm forced into changing my site layout, I'd like to know if there is a custom solution.
In short no! Unless your site is so niche that advertisers approach you - even then breaking conventions is hard work (I've tried!).
Take a look at the interactive advertising Bureau's standard sizes, perhaps something will fit.