Google Images

A search engine with thousands of mind map images, but with no organization. You can get some filtering by appending keywords related to what you want; for example, try 'mind map project' and 'mind map meeting'. Also, keywords "mind map" and "mindmap" return different results. Some images, though labeled so, are not really mind maps.

Topicscape

A good collection, organized by categories, like creativity, marketing, medical, planning, sales, and so on.

Mindjet

MindManager original mind map files to download, organized by categories: project management, enterprise, quality improvement, students and others. Get the enlarged picture from the screen or get the files and download the free viewer to see them.

Examples of Illumine Training

Mind maps of some problem-solving strategies and books.

Buzan Australia gallery

Hand-made mind maps about mind mapping laws, learn a language, creative thinking and some others.

Mindmappedia.com

What seems at first a good idea was messed up by a bad implementation: searches with low precision, little useful information in the results, cropped and huge mind map images. You may find something useful there anyway, but... good luck!