Aptdate is a nifty jailbreak tweak that will notify you when a Cydia package you have installed has an update available. The cool thing about Aptdate tweak is that it uses Apple banner notifications to give it a apple-ish stock look.
The tweak comes with a simple preference pane. You can choose how often to check for updates and whether to enable of disable the tweak all together.
You can download Aptdate via Cydia for free. One last quick tip, the more you choose to check for Cydia updates the more your battery will be drained.
Banner notifications for Cydia package updates are finally here! This tweak checks the stock Cydia repos for updates in the background and alerts you if any of your packages require updating.