I just found this site, and it's pretty cool. The design is a bit early 2000s, but the results are very cool. You enter your name (or whatever other text you want to use), pick a font (there are tons), pick a color, pick a size, and pick the slant you want your letters to be written on. The site then generates a very cool signature for you to use on websites, blogs, whatever. You can save the signature as a picture or generate HTML or BB code to use it on blogs or forums. They'll even create an animation of the signature for you, but that costs $20.
MyLiveSignature.com
[found via Livehacker]
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