Google Maps...

okay - picked the easy one - but it really is great.

It is a Java app that shows you Google Map basically.

It makes great use of the number pad on the phone as shortcuts.

The functionalities you have:

Pan and zoom

- just like on the web

Find Business, Location, or Directions

- remembers your previous searches

- once location is found you can call the place (if it is a restaurant for example), get directions to and from there or save as favorite + you can see details about the place

- If multiple locations are found you can cycle through them using the number pad

Map or Satellite view

Clear Map

Show traffic - now this is cool :)