I was goofing off online the other day and came across Google's Custom Search Engine. Creating a CSE allows you to leverage the power of Google's search engine while keeping the search constrained to a very small subset of sites. This can be especially useful if one of the sites you use frequently has very poor searching capabilities (ahem... I'm talking to you reddit.)
If you are interested in extending what I already have or want a jumping off point for your own project, you can check out the code for StackSearch here.