I've wondered when a general-purpose web engine(s) would begin offering a "roll your own search engine" service.
No more wondering, say hello to:
Gigablast's: Build Your Own Topic Search Engine.
It's now possible to create a subset of the complete Gigablast web index that ONLY searches the sites (or subsites) you specify. You can select up to 200 urls.
Simply copy and replace a few lines of code, list the urls of the sites you want your topic engine to search, paste the finished code into a web page, and you're done. You do not need to register and you can create as many topic engines as you like.