Wi-Fi Sync is a clever little app with a self-explanatory name: It allows you to sync your jailbroken iPhone to iTunes over Wi-Fi. While it did not get approved by Apple, it is available in the Cydia store for $10.
One thing I've always been a little iffy about was paying for apps via jailbreak. The fact that I couldn't back up the apps on my computer was the reason I avoided trying out any of the pay stuff when I jailbroke my phone.
My question is, if something were to happen to your phone, and you got a new one and jailbroke it again, could you reclaim a Cydia pay app without paying again as well?