To learn more about Gravatar please visit http://en.gravatar.com/.
This is a very simple asp.net C# user control which will spit out a gravatar image. All gravatar options are included in this package.
You can choose to use a default image if no email is fond (silhouette, blank image etc) or use a generated one from Gravatar (identicon, monsterid, wavatar)
Happy to fix any issues you encounter or download the source and alter.