Many of who are creating web banner for clients are either always referring to various sites for sizing, or have little notes around that have the sizes of the banners, or in some cases you have every size there is already saved in a PSD file so its right there and ready for you to copy and start working on.
Well here is our sheet that lists for us the common and not so common web banner sizes that are out there, in short order we hope to have uploaded as well simple PSD based files for you to download as well, so look for that in an up coming post.