The are tons of threads about this subject but what the hell.
These are Hacks and Apps that I use.
Backgrounder, not much to say. It does what it says.
Activator, maps button actuations and screen gestures to typical iPad functions. My favorite is holding down the Home Button to Reboot iPad.
ProSwitcher HD, card style multi-tasking.
SBSettings, access toggles from the Home Screen.
ScreenDimmer, sets the time before the backlight dims. You can also set the time before the screen locks.
iFile, a must if you want to access the iOS file system.
Virtual Memory, this is not a Cydia app but a file hack. Page File Goodness.
OpenSSH, it by itself is not very impressive but with iSSH from the App Store gives you the iPad version of MobileTerminal.
NetaTalk, for Mac users only. The easiest way to SSH into the iOS file system. Just make sure you change your root password. And the only way to do that is to use OpenSSH with iSSH.
3G Unrestrictor, I don't use it much but since I have it installed I might as well mention it.