aCalendar: Works ok, no force close (fc), shows my contact's brithday's without any need to configure that (may it synchronized with my google's calender, do not know). Interesting app to have installed.
Advanced Task Killer: Quick way to close apps, helps preventing apps from wasting battery.
AirDroid: Control your Android from any browser. That is usefull to use a laptop's keyboard to type SMS or exchange files to/from the phone for instance.
AndChat (Free): For those who still use irc this is really good irc client.
Andro12C financial (free): If you need to calcule amortizations this is very handy calculator.
BusyBox: Command line for Android, very useful when used together with 'adb shell' command from a laptop.
CamScanner -Phone PDF Creator: Scanner app. I was not very faithful about this app before I tried it. It really did a good job in my tests, the app crops and tries to undo image distortions (because of shaking hand) so the final image is a perfect rectangle, I was not expecting it to do that. The final result is really good as long as you can make the camera to correctly focus the paper. In my case I enabled macro focus, anti-shake and configured the camera to focus on the part of the paper that has letters in it (if you try to focus a empty part of the paper the camera does not correctly focus).
Coffice: Calligra Office from KDE :-) I am a KDE developer so this is a bias review hehe. However I am not a Calligra developer so do not ask me any details about its source code because I do not know. This apps reads OpenOffice/LibreOffice documents, I have not tried to open Word or Excel documents but I guess it is capable of it too. The installation takes more than usual space because it needs to download Qt libraries (Coffice is written in C++, so it is not a native Android app, which are usually written in Java).
ColorNote Notepad Notes: I had to find a new one after I installed Chameleon in my Samsung Galaxy S2 since Chameleon does not come with a note app.
CPU Spy Plus: Usefull for detecting if the CPU is not in deep sleep, which usually means some app is taking CPU and consequently battery power.
English Dictionary - Offline: English dictionary, handy.
GetRIL: Test if the modem driver (the one used for 2G/3G audio and data connections) matches (is suitable for) the library (called ril) Android uses to handle it. If they do not mach it can mean the modem may not be using some features to save power or even the modem is not working properly. My current ril does not match my modem's firmware and I have not seen any real issue yet, so do not take the words above as a garantee of problems if the modem and ril do not match.
File Manager: Advanced file manager for advanced users :-) Allows mounting /system as read-write if the firmware is rooted. Just do not mess with files in /system or you will have to re-install Android. In case you mess with /efs even re-installing Android will not be enough to make the phone works again with your operator's network. Be carefull.
Globo News: This one is for Brazilians or anyone that can listen to Brazilian Portuguese. This is an app that receives video streams from the biggest Brazilian news tv channel (kind of a CNN for Brazil).
GSam Battery Monitor: Shows how much battery each app or system component used, also estimates how long the battery is going to last until needs to be recharged. Very handy for battery hungry apps users or just to identify why the battery does not last long.
MoboPlayer: Video player. Plays mp4 and rmvb, which are the most interesting ones for me, probably plays other formats too.
Network Monitor Mini: Show download/upload speeds on the screen all the time (it is always visible). I like to see in real time how my operator network's speed varies, just for curiosity :-)
Network Signal Info: Another app just for curiosity hehe. Show signal strengh for wifi and cell radios with graph.
Nova Launcher: App launcher, I like this one better than the default aokp (Android Open Kang Project) one that comes with Chameleon.
Offline dictionaries: Offline translation dictionaries (includes English <-> Brazilian Portuguese).->
Palmary Weather: Weather app with detailed weather information, such as hourly weather forecast. Very cool.
Pianist HD - Finger Tap Piano: Very cool piano app, try it.
Screen Filter: Creates a shadow to make the screen darker. Theoretically that helps saving battery for oled screens (does not work with TFT screens used in Sony's phones for instance).
Speedtest.net: Another diagnostic tool, this one measures network speed and is probably well known by many people.
Titanium Backup ★ root: Very handy app to backup other apps and their configurations. Android already saves Android's apps list on your google account, but as far as I can tell it does not stores apps configurations, so this one does all the job you need to fully restore your apps after a firmware re-install for instance.
TrackID™: Play a small sample of any song with this app opened it will (if there is Internet available) detect which song is being played. Very cool.
Trainer PRO Run, walk & bike: I like riding a bike and as a curious person I wanted to know how much time, how far and how many calories I spent when doing my usual bike circuit.
TuneIn Radio: When I get bored with my in the air fm radio app I like to use this one to listen to other radios :-)
WiFi TXpower: Decrease (or increase) wifi card's tx power. Decreasing tx power helps saving power and if the access point is very close (a few meters without any wall in between) that also helps decreasing radio interference. Increasing tx power helps signal strength if there are obstacles between the phone and the access point.
Z - Device Test: Diagnostic tool, shows a lot of details about the device, very interesting.
ZEDGE™: Allows downloading wallpapers, ring tones and other stuff to customize your device. Very cool.