on my iPod touch 4gen:
slacker radio -- can also cache stations for when you don't have connection
CalenGoo - calendar interfaces to google calendar so you have web access too ... handles stuff stock calendar doesn't do well (like repeating events)
GroupsFree - arrange contacts into groups (family, clients, whatever)
Paperless - checklist (very good app)
eWallet - I use for secure storage for all my client passwords, contacts, etc.
Hours Tracker - use for recording time spent on service calls (email CSV to desktop, then import into my database)
Scany - wireless network tool, IP address & port scans, etc.
MSD Ignition - database of install instructions, wiring diagrams, etc
Skyview - star app - point at sky, it ID's what you are looking at (PIA to calibrate, though)
Bible - (youversion)
CH Lite - construction calculator
TPE (the photographers ephemeris) - sun/moon rise/set times, phase, bearings, etc on map
5-0 Radio Pro - scanner
iHam Locate - repeater database
Dilbert - 'nuf said
Tapatalk, of course