Cem Sisman created a ASP.Net image cropping control for the JQuery plugin, Jcrop.
- ASP.Net Sample (with IE8, run in compatibility mode)
- ASP.Net Fixed Ratio (with IE8, run in compatibility mode)
- Jcrop Preview Thumbnail
- Jcrop Live Demo
Matthew Paulson has a quick and dirty write up on how to implement this on your page too.
The codeplex project needs to be updated to correct some IE8 issues but I'm hoping all you need to do is download the new version of JCrop and everything should be fixed.