HotBot Graphical query-building aids and a large Web index make this a popular site. Northern Light has advanced search features which lets you refine your search. You can construct very specifc and detailed queries using this engine. A popular site which has a great number of categories. Good place to start a search.
Searches tend to return a large number of sites.
For very specific terms, you might have better luck with AltaVista. TechCrawler ,as you might guess from its name, is for tech pros. All results come from the Web's top tech sites. It will construct a query and submit it to multiple search engines. Returns are arranged by search engine.