Here's a quick, simple site:

http://www.shrinkpictures.com/create-avatar/

It resizes images, and gives you some simple choices for cropping (center, bottom right. etc). You save the avatar to your computer, then upload it here.

If you've got a Facebook account, that's another option. It lets you create profile pics from uploaded photos, and you can crop
them with its built-in editor.

Hope that helps someone down the line,

Mark