Blog Badges/Buttons and Avatars
The standard size for blog badges is 125×125 pixels. Occasionally you will find larger, but you have to keep in mind that most blog layouts will only accommodate 125 pixels wide. You can go longer, but I’d say no more than 125×250 pixels. If you go wider, you might “break” peoples’ layouts. And most bloggers don’t know how to resize the image, so you need to provide it exactly how they should use it.
Blog badges (also called buttons) can be displayed on your blog, along with a snippet of code, so that readers can take your badge and display it on their blog. This is free advertising for you! Also, if you intend to do giveaways on your blog, requiring entrants to add your badge to their blog is a good method of getting entries.
If you have a blog badge that is 125×125 (or any other square like that) you can also use it for an avatar on social networking sites. Yes, you can use rectangular images, but some of it will get cut off on the longer sides.
Even if you already have a blog layout with a cohesive look, I can create a blog badge for you that will match. Blog badges and avatars cost $4.