Image based links in primary links menu or similiar

http://drupal.org/project/imagemenu
I've never used it and can't personally recommend it... give it a try if you like though.

However, unless you need "unique" images per menu item and have a very good reason for using inline images for it, this is a bad approach. CSS background images are a better choice. See: http://www.google.com/search?q=css+image+replacement
If you still need unique images per menu item and want to do it in the most standards compliant, accessible, and SEO-friendly way... still use CSS backgrounds as suggested, however you can get a custom class per menu item using http://drupal.org/project/menuclass