It's fitting that O'Reilly's OnLamp.com has a new tutorial on creating your own mini-search portals, what Google calls Custom Search Engines. We first took a look at this last fall. You don't need to know any Google API tricks or special URL combinations to build a Custom Search Engine. Instead, Google gives you a 2-step wizard that lets you narrow down the pool of results to just a particular domain or a certain keyword set (so you don't have to type in the same keywords all the time). You can also tell it to prefer results from certain domains over others--handy.
This is great for finding out who might be plagiarizing your blog (some folks are dumb enough not to strip the byline from material they've leeched from RSS feeds without appropriate acknowledgement). It's also handy, if you need to keep track of media reporting and blogging on a particular subject--just fire up the custom search engine to see what's up. This makes a custom search preferable to a blog tracker such as Technorati for staying on top of new content about a particular keyword, since Google's search results are updated frequently and contain content from more than just blog sites, like Technorati.
Some other good Google Custom Search examples include STEM, the Digital Camera Review Guide, and the Canadian Finance Blog Search.
Google Co-op is a service you may have heard a bit about, and may have simply overlooked... I know I did at first. The idea is that you can give it a list of sites that have information pertaining to a very specific subject, and create a little search engine based on only those sites, filtering out everything else. 
