My list:
Angry Birds RIO
9GAG
AdFree(if ROM doesn't have AdFree pre-installed)
AnTuTu Benchmark(testing ROM speed, stability, etc)
Blackmart
Aptoide
AppBrain
Block Puzzle 2
Opera
Chess Free
CPU Spy
Defender
FasterFix(for root users)
Facebook
Fruit Ninja
Flash Player
Go!Chat
GPS Status
LINE
Google Plus(Not really using)
MX Video Player
PAPAGO!
Plants vs Zombies HD
Real Player
Reversi Free
Root Explorer(for root users)
Titanium Backup Pro/Basic
TurboFly 3D
Unblock Me FREE
Voodoo Control Plus/Basic(for SGS rooted users)
WhatsApp
XDA Premiuim
Voltage Control(for OCing)