DuckDuckGo: Doesn't look bad - could replace Google for some searches => trying it out... .
Gigablast: An alternative search engine.
Snap!: A very alternative search engine.
KartOO: A search engine (uses other search engines in the background) which relates the hits to themes. Nice!
Mnemomap: Similar to Kartoo (still in beta phase).
Google Trends: See when which keywords where most used for searching in Google.
Midomi: You remember a song and would like to know its title? Go there, sing or whistle it and you should get back its name.