Twivatar is a RESTful API to a Twitter user's avatar built out of frustration of external Twitter apps breaking when the avatar url is stored, and then changed by that user later on Twitter - the result is a broken image on that app unless they constantly check for profile changes.
<img src="http://twivatar.org/[screen_name]" />
Alternatively you can specify the size image you want from:
- mini (24x24)
- normal (48x48 - default)
- bigger (73x73)
<img src="http://twivatar.org/[screen_name]/[size]" />