I am assuming you have an android phone
if you need to track a vehicle expenses or gas consumption or matinenace reminders then acar is by far the best.
Convertpad is probaly the best conversion application for converting anythgin such as distance, area, volume , land area etc,
If you need to have notes and stuff on the go then evernote is the best you can have a pc client as well and they will sync. You can add pictures, text notes, documents anything
If you ship or recieve alot of packages then packag.e buddy is a very good app.. will let you know where your package is..
Printershare is a very good app.. it has a pc client so that you can print documents on your printer through your pc at home. You can print anywhere the job goes back through the internet to you rprinter or through your wirless at home.
Realcalc is a good free scientific calculator
shadyface is a nice app.. when you run it it will record any voice. YOu can set your phone down in a meetingf or what ever and record the meeting
scan2pdf is a very good app. You can take a pic of a document or whatever and then it converts to pdf. so you can email or wahtever. Suprising it is very good at documents.. can take a page out of a book and its very readable.. in fact it really amazed me.
Photoexpress is a good pictured editor .. very advanced in capabilities.
Documentws to go is the best ms office app.. its costly though at $14.99 but in my bvusiness i needed to be able to edit and produce word, excell etc documents
GPS status is one of the best gps apps I use it alot in my work.
ESfile explorer is agood app, you can map to your home network drives and copy files back and forth..
ebuddy is the better chat ive found so far.. does facebook, msn, and yahoo, etc
Those are some of my better ones.