Niche marketing

We recently received our copy of the Internet Retailer 500 at Discovery. It's always fascinating to see some of the varieties of retailers that are out there. I saw a post from Central Vacuums on their blog about being #495. I'd never even considered the idea of a centralized vacuum system. Two of the most useful pages on the top 10 results in Google for Central Vacuums were a buying guide, and BuiltinVacuum.com, which linked to "7 reasons to install a central vacuum cleaner system in your new or existing home" across the top of the page.
Any other intriguing retailers out there you've noticed?