Almost every thread from the search "Must have apps" came back with App World posts. I'll start by listing the very few apps I have gotten so far. I'm curious what everyone else uses.
(Peal 8130 for me if that matters.)
Aerize Card Loader 2008
BBSmart Alarms Pro
Berry Buzz
TetherBerry
vPost
Yatca*
Where (GPS Twitter*)
I haven't goten Yatca/GPS Twitter yet because I'm not sure of their interaction with each other.