I really like Android and I'm on my second phone (HTC EVO) and been using them for going on two years. Here are some that I like.
Fring: Video phone but you really need to be on WiFi for it to work great.
TiKL: It makes your phone like a Nextel. It's a push button walkie talkie program that works pretty darn good.
Astro: It is a file explorer program that does other things too. Has a tool to back up all your programs so you can save them to the SD card instead of having to down load them all again if you hard reset your phone.
Battery Indicator
Bump: Allows you to transfer pics, contacts, and apps to other Android users.
Bubble: Is a fairly accurate level once you calibrate it.
Caller ID Faker: Lets you call someone up to 2 minutes (for free) and specify the number that the caller ID will show. You can also disguise your voice to male or female and it actually sounds pretty realistic. Awesome prank.
ES Task Manager: Have to search for just task manager to find it and it has a little gear and window as the icon. Best task manager I have found for killing programs and it has a auto kill that works good to kill programs that like to open on their own all the time.
Final Countdown: Is a countdown timer you can put on your home screen. I have my wedding date programed on mine.
Juice Defender: You NEED this! I just found it and it is making my battery last almost 3 times longer. It shuts down your data connection when it isn't being used and makes a big difference on battery life.
Lookout: Is a virus scanner, a call log and contacts back up, and if your phone is lost or stolen you can track it on a map or make the phone 'scream' so that you can find it (works even if on vibrate).
Nesoid Lite: Nintendo emulator. You have to find the games. I downloaded a file with I think over 6000 games.
Radar Now: Small quick program for showing local radar. All it does.
Shazam: listens to a song and then tells you what it is.
Spare parts: Gives you various phone statistics like amount of processor time since last charge, and time that screen has been on since last charge. Gives a good idea of how much use you are getting from a battery charge over just how long the battery lasts since you charged it.
VoiceBot: Make your phone say what you type. Can cuss out your friends with your phone and make it say 'dirty' words.