wikipedia

general search alternatives:
viewzi: a lot of different ways of seeing and searching through data
mnemomap: nice interface with semantic map and a variety of tools
searchme: turns web search into quicklook visual browsing, a little too sexy for its own good
bryns brain: another sexy interface with web previews
touchgraph: uses Java to visually displays results from the Google search API
research beyond google: some useful resources for doing academic or statistical research
textmap: visualizes tons of data related to search topics or issues (news histogram, relational network, juxtapositions)
a couple of categorizing engines: grokker, clusty and quintura