SBSettings is always the first tweak I install after jailbreaking. Even when it's not installed, I find myself swiping at the statusbar expecting a menu to drop. The simple utility gives me quick access to toggle Wi-Fi and Bluetooth settings, as well as a respring function.
Though I've yet to find anything in Cydia that matches the functionality of SBSettings, the competition is certainly heating up. Jeff recently told you about Homescreen Settings, which places the actions on your springboard. I'm going to tell you about SwitcherSettings, which adds the functions to your app switcher...