ah... too hard to chose just 5 ;p
mmmm lets see..
Barrel
winterboard
sbsettings
MyStrings
OpenSSH
all jailbreak ones lol.. app store i never use to download apps, i have a few free sat nav that does not find any addresses and flashlight that comes in handy but none compare to the tweaks you find in cydia and i use app store mainly for games.. the app store is amazing for games and bad for apps while i dont really download games from cydia apart from the mega drive emulator and the snes one