General Search - General web search tools are your "regular search engines" like Google, Bing, Yahoo, etc.
Weblog Search - Blog Search engines search for blogs, feeds and posts
Web Directories - Directories are valuable research tools that categorize links to websites on the web to make it easy for a user to explore a specific topic.
Deep Web and Library Search - Deep web search engines search the "invisible web," which are pages not indexed by general search engines. This content includes (1) disconnected pages, (2) pages consisting primarily of images, audio, video, (3) Flash, Shockwave, and compressed files, (4) content retrieved as a result of filling out forms, (5) real time information (although general search engines of recently started indexing this type of information), and (6) pages that are proprietary. Library search tools are comprehensive library databases that have the ability to return and display print and electronic resources.
News Search Tools - These tools search for the latest news by indexing articles and similar pages across the web. They are very useful for finding news from reliable sources.
E-Mail Alerts and Page Monitors - Email Alerts are services that provide "email alerts" whenever a user-specified set of search results changes. These types of alerts can be built using a number of different queries. Page Monitors are used to track changes to a user-specified page. They are useful for tracking "static" pages, as well as those that aren't updated as frequently.
Video Search - Video search tools search for video content (self-explanatory). This can be done through a web video search like Google Video or a site-specific search like Youtube (which usually searches user-uploaded content).
Image Search - Image search tools search the web for indexed images. These search tools can be general image search tools found on major search engines or tools that search a large database like Flickr (which strictly hosts user-uploaded content).
Tag-Based Sites - These sites include social news and social bookmarking sites which "tag" its content.
Meta-Search Engines - Meta-Search engines combine multiple search engines into one convenient display. There are two types of meta-search engines: (1) unified and (2) integrated. Unified search engines combines the displays of multiple search engines, while integrated search engines integrate search engine content into one set of search results.
Google Custom Search Engine - A Google custom search engine created through the Google search engine. You can read more about this customizable engine here.
