(Blogger Buzz) If you're using BlogThis! now, you should see the bold, italic, font color, link, and blockquote buttons already. If you're not using BlogThis!, you can get it by following the instructions in our help article, or by enabling it on the Google Toolbar. (Click "Options," go to the "More" tab, then click on the "BlogThis!" checkbox.)
I'm using it right now, and it seems quite useful. A recommended tool for blog surfers everywhere!