Here are my top 15
APW Widgets- Best looking sense-like widgets
MyBackup Pro- Personally, I like it better than Titanium Backup. Much easier for me.
SwiftKeyX- This is by far the best keyboard app on the market. Way better than stock.
App2Sd Pro- Best app of its kind.
Juice Defender Ultimate- Extends battery life a bunch
PullDown App Drawer- For those using MIUI, it is great!
Sixxaxis Controller- This is ridiculously cool
Sd Card Speed Booster- Increases speed of phone
Wifi File Explorer Pro- Saves me the hassle of looking for a USB cable
Astrid- My favorite Task Manager.
FPSE- Who wouldn't want to play PS1 games on a phone?
N64oid- Same ^ but with n64..duh.
Gameboid- For reliving the childhood.
PowerAmp Music Player- Way better than stock, plus a very good Equalizer
Soundhound- for that moment when you think "That song is awesome, i just wish i knew the name.