Most of everything on here is free. If it's not free, it's because I feel it's totally worth every penny. This post is unfinished.
Barcode Scanner (free)
Anyone who has a mobile device with an autofocusing camera needs to have a barcode scanner. Normal barcodes are boring, but here I'm talking about QR Codes. They are 2d barcodes that hold messages and links to offers or websites. They are getting popular, wise up to them.
ES File Explorer (free)
A handy tool for getting into the filesystem of your droid considering mine didn't come with one.
Es Task Manager (free)
This task manager keeps power hungry apps at bay by visually showing you whats running. Also, a handy desktop shortcut widget for killing all whitelisted apps :)
Need to translate spanish to english? Need to search for a book, movie or product? Take a picture of it! Google is pretty smart and uses really smart monkeys to deliver your results.
My Tracks (free)
Need to keep track of a route you take when biking or jogging or whenever? This utility does just that and plots it all on a google map. Is niice!
SMS Scheduler (free)
Ever need to send a text and a specific time and fell asleep? This app prevents all that mess. Send a text whenever you want it to be sent.
A very fun and addicting multiplayer game. The basic premise of the game is to get rid of the other player's marbels by knocking them off the platform, into holes or blowing them up. Beware of the new Cestos 2 as it's in BETA and has been buggy lately.
Team up or play against your friends. Steal bases, build troops and ships, it's all out war!
Robo Defense (free basic, $.99 full)
Keep waves of troops, tanks and planes from entering your base. Build and upgrade towers with an endless difficulty rating system.
Angry Birds (free)
The pigs have stolen the eggs from the hen house! You must slingshot birds to destroy the pig villages and get your revenge!
Share location information with trusted friends. This is an opt-in service and doesn't follow your every move. Many businesses are starting to offer specials to people that become "The Mayor" of that location by visiting there more than everyone else.
Grooveshark (free trial period, $3/mo afterwards)
Grooveshark is by far one of the best music streaming jukeboxes on the web. It is now also on mobile devices and packs just as much power. You can even build playlists on your phone or pull down songs for offline play. Totally worth the subscription fee.
Google Listen (free)
Are you into podcasts? This free app will keep your podcasts up to date! Search through the categories or browse whats popular.
Rock Player (free)
The best video player I've found so far. It's free and plays more videos than the phone could when I un-boxed it.