Duck Duck Go
N.B This isn't related to the official DuckDuckGo app.
Integrates the search engine DuckDuckGo with the Android OS. It adds another web search provider to the system and some neat suggestions for the user.
There is an option to use DDG in the CyanogenMod 10 browser (depending on the locale), and also in Tint Browser.
Firefox allows you make search engines by long-pressing any input field.