Custom types can be leverage for anything that can be repeatable. So as you said a gallery or portfolio would work very nicely. I’ve already used them on a few different projects:
- Recipes
- Employee Roster
- Callouts for the homepage
- rotating sliders.
Other ideas are:
- products for a commerce site—The custom taxonomies would make for some powerful option for each product.
- For custom sidebar content. Y
- An Ad manager.
The possibilities are really endless. Anything that can be seen as a collection is really what this is for.