Here are a few cool apps people can search the Marketplace for. All free.
SpecTrek Light - Augmented Reality ghost hunting game.
TaskPanel - Best Task Manager I have found.
CardioTrainer - Does a bunch of stuff but I just use it for the pedometer.
Bubble - plumb/level
My Tracks - records GPS tracks.
GeoBeagle - Geocaching app. Been using it to set my own waypoints.
DroidTracker - SMS your phone and get the phones location back. Great if my phone gets stolen.
Movies - Showtimes, trailers, reviews.
Listen - Subscribe, download and stream podcast.
Unit Converter - Unit converter.
Finance - stock quotes
Ultimate Stopwatch - Stopwatch and countdown timer.
GPS Status - Does a bunch of stuff but I use it for a compass.
Note Me - Notes.
DockRunner - Droid ONLY. Turns on the clock/weather/slideshow/music app that is active when attached to the Motorola dock.
USA Today - news, scores and weather. Best weather app I have found.
NetCounter - Traffic counter for EDGE/3G and Wi-Fi.
Ustream Broadcaster - Stream live video to the web. So cool.