A comment on bql about the John Gay Photographic collection at English heritage -http://tinyurl.com/cmk5a2 brought to mind the fact that I use several photo libraries (as an alternative to my own lack of photograpic skills) . The problem is always - where do you stand with regard to copyright.
I've mentioned www.sxc.hu before on this blog, but increasingly I'm using a flickr search engine called Compufight It works with Firefox and IE7 but struggles on IE6. You need to make sure that the Creative Commons setting is set to only 'only' before carrying out a search, and even then if you're planning to exhibit or sell any work derived from the photo it's worth checking out the exact terms under the Additional Information heading in the bottom right of the page.
This image by Darwin Bell