If you’re interested in stock photos, or just like browsing good ol’ Creative Commons content, check out Everystockphoto.com (http://everystockphoto.com.) At the moment they’re indexing over 260,000 CC, public domain, and other “attribution-licensed” photos. They’re also adding photos at the rate of about 20,000 a week.
Searching is by tag when possible, though other information about the photo is indexed including description, keywords, and title. I did a simple keyword search for slug and got 23 results. The initial page of 15 results included photographs from Flickr, stock.xchng, and morgueFile. The results page includes thumbnails of found photos, icons to indicate license (CC, Attribution, etc.) the (pixel) size of the full photo, and the source.
Click on the thumbnail for larger photo, additional information, and pointers both to the full sized photo and to the page where the photo originally came from (because you don’t want to miss all the comments on the photo of the giant slug next to the sunglasses.)
You can do searching without being logged into the site, but if you register with Everystockphoto.com (it’s free) you’ll get additional goodies including access to a forum and the ability to tag photos.