Gesture Search: This should be on your home screen. Do it.

[ShiggityX2]

Gesture Search is absolutely essential for me to effectively search through my 800+ imported contacts from Gmail and Facebook. Powered by Google's tried and true search power, I rarely have to draw out more than 2 letters before the correct contact is at the top of the list. From there, selecting a contact will take you to your address book entry for that contact. Simply use your finger to trace a letter to start spelling out your search. Tracing a horizontal line from right to left will delete the last letter entered, and a line from left to right will clear the entire field.

Brilliant, simple, and extremely useful.