iSHSHit!

TinyUmbrella saves the "SHSH blobs" of your Apple device (i.e. iPhone, iPod, or iPad), allowing you to bypass Apple's servers and downgrade your firmware through iTunes, whenever you want. Your device does NOT have to be jailbroken for TinyUmbrella to work.

redsn0w is a utility that will jailbreak your iPhone or iPod Touch, allowing it to run apps that are not approved by Apple.

PkgBackup is a backup application for jailbroken iPhones that backs up & restores all of your Cydia apps, your Cydia sources, and even your homescreen layout. Simply sync your backup with iTunes or Dropbox- then, when you update or restore your device, bring back all of your Cydia apps by redownloading PkgBackup afterwards.

iFaith is a program that can save the SHSH blobs of the current version of iOS that's running on your jailbroken iPhone. It will work any version of iOS, whether or not that version is still signed by Apple. Saving your SHSH blobs allows you to restore your device to the saved version of iOS at anytime, even when Apple has stopped approving restores to that version.