...some creative alternative search engines

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

shopping tools:
like.com: find apparel and accessories by color, shape or pattern
crispy shop: nice product comparison engine

wikipedia search tools:
powerset: fast searching with some nice preview features
wikimindmap: mindmap search wikipedia articles

but if you are going to use Google...
here are some valuable tips and tricks:
Google Hacks: how to do search for synonyms and number ranges, etc.
Top 10 Obscure Google Search Tricks: some less known google search keywords