250+ Solitaire Collection
I have tried the beta (or maybe alpha) version of Firefox. Even for an alpha, it really doesn’t work - yet.
+1
The acoustic and EM scans are interesting. What are the others?
How come I can’t find “tricorder” or “moonblink” in Android Marketplace from my HTC Hero? I’m in Taiwan if that makes a difference.
Some of my favourites have already been mentioned, but I’ll say Google Sky Map again despite the fact it sometimes goes all strange on my HTC Hero - I think it’s about how the phone is held…??
Spotify might do the same as Pandora, but not sure. LastFM too. I never used either of them.
FartDroid is worth a go if you are as juvenile as me - you can preset it to make a fart sound at any given time, then leave your phone hidden somewhere. Can’t wait to use it at the family Christmas!
FXCamera is better than RetroCamera, IMO, more user-friendly. The Android version of Hipstamatic.
Very London-centric but I have apps that give me up-to-the-second tube status information, and one that uses Google maps to tell me where the nearest Oyster top-up is(for my Oyster travelcard).
And I like the free memory games.
Coincidentally, the beta has become available today. I’ve just downloaded it, and all I can say this early is that it seems to work.
GRAV measures velocity (move your cell around and watch the chart)
GEO is the compass (tap bottom of screen) and GPS coordinates
EMS displays cellular signal strength and available wifi
SOL is solar flares - not live data of course.
Perhaps the app requires a higher version of Android than what you have on your phone.
Unfortunately, it doesn’t work over 3G in the US. Only on WiFi.
I recommend Where. It’s similar to Yelp but has a few more features.
Most of my favorite free ones have been mentioned.
One that hasn’t is the Yelp! app. I tried a bunch of different similar apps but Yelp tends to get me the most useful results the most often.
I use the barcode scanner more than I ever expected I would. Same with Google Goggles.
I like AppBrainbetter than the standard Marketplace app.
One that isn’t free but is cheap and freakin invaluable (to me at least) is Tasker. (Life Hacker review that convinced me to shell out the bucks here)
Not an App, but getting the Swype keyboard is also something that I consider to be essential to the android phone experience. Depending on what phone you have you may already have Swype as an option, or you might have to try to get into the Beta or get an unofficial version.
It’s a neat little app, isn’t it?
Ahem. Well then, consider it a seconding. 
Abduction! - game
Age of Conquest - game
Air Control Lite - game
Alchemy - game
AndChat - irc chat client
Antigen - game
Astrid Tasks - task prioritizer, note keeper
Bump - sharing files
BuzzFeed - fun on internets
Carrr Matey -finding your car in a large place
Cheezburger - I Can Haz Cheezburger aggregator
Congress - really nifty Congressional watchdog application
Compass - it’s a compass.
Google Earth
Euchre
Yahoo Fantasy Football
Google Goggles - never actually got it to work right
Golf Channel
Google Sky
Google Translate - super helpful when you need it
Huffington Post
IMDb
Mahjong
Google Maps
Google Navigation - I use this religiously
NPR News
Photoshop Express
PicSay - same as Photoshop, mostly. It does things Photoshop doesn’t
Real Blackjack
ESPN ScoreCenter
Google Shopper
Opera - solid browser. I’m not entirely sold that it’s faster than the stock browser, though. The stock one is pretty frickin’ slick.
Shortyz - great crossword application
Slot Machine
StumbleUpon - Internet hijinks
Sudoku Free
SuperYatzy - Yahtzee clone
The Weather Channel
Traffic Jam - logic puzzle
United States Constitution
Virtual Vuvuzela
Whoopee Cushion
WordUp! - anagram game
xPiano - virtual piano. i can’t play it, but it’s fun to annoy with it.
Zombie, Run! - fun zombie game
I started a thread in Cafe Society that will soon sink like a stone, I’m sure.
But anyone who has a Napster account - there’s a new Napster app for Android and Apple. I’m just so excited because now I can drop iTunes out of my music needs and go back to Napster alone, like it was before I got the damn iPhone. I’m soooooo happy!
(So, the app is free, but you have to have a subscription)
HAPPY!!!
I have been thinking about starting one of these, see some I know and I am now in love with the Tricorder. 
My choices for inclusion:
Gesture Search: Google app, you can search through your contacts, Bookmarks, Apps, Music, and/or Phone Settings by writing the letters on the screen. Makes it very easy to find thing on your phone without going through lots of menus.
Soundhound: Music identifier, much better than the VCast that Verizon has. Limited to only 5 full identifications a month unless you buy, but ti has many other features that are also nice, including links to lyrics and buying songs.
iBird Lite: Demo for iBird Pro. Has 30 birds, including sounds, images, photos, search engine, all kinds of information and ways to identify birds, make notes on them, etc. Makes me want to get the Pro version when I have the extra $20.
Unit Converter - Convertpad: You want to convert feet into centimeters? Anything can do that. How about the volume that 100 board feet of lumber takes up? in cubit meters. Or how much the Croatian kuna is worth compared to the Malasian ringgit? Seriously, it has everything from common units for metric/imperial conversion to Henry’s Law, to Molar concentration to thermal conductivity. I have no idea what most of the conversions mean, but it is fun to play with.
App Categories: for organizing my apps and not running out of Home screen space.
TxtPad Lite: Nice little text editor for when you want to write. Not limited to .txt files, can also open and save .html, .xml, etc…
DailyStrip: for keeping up with part of my daily comic strip addiction when on the road.
Questionable Content Browswer: Devoted to just the QC comic strip.
Angry Birds Lite. It’s only in the Beta right now, but the official release is coming this week. Very fun little game. After playing the Beta a lot, I will shell out for the full version I’m sure.