for my droid-
Advanced Task Killer - manually closes selected programs when not in use
Lookout - anti-virus
United States Constitution - has the entire constitution as well as a number of historic speeches, Articles of Confederation, history behind the constitution, etc
Voice Recorder - great for quick voice notes or documenting a situation.
Colornote - a notepad app
Right2Bear (had to pay $3 for this one) - can look up reciprocity information on concealed carry permits by state - it does leave out some info, mostly pertaining to non-resident permits, and open carry
And a couple sound board apps - Homer Simpson, Evil Dead (Bruce Campbell), and Samuel Jackson
edit: I now also have all the free ones Adondo listed. I like the Tricorder!