iSHSHit is a new Cydia app which allows you to save and backup SHSH blobs directly from your iOS device. It also send your saved SHSH blobs via email, which is a very good feature. Also automatically saves your SHSH blobs on Cydia servers using Cydia On-File service. iSHSHit is available from Cydia under the BigBoss repository for free.
Here is the official description:
iSHSHit allows you to back up device firmware SHSH blobs from Apple directly on your device for later downgrading. It automatically uses the Cydia On File service in the background, so it’s a great way to ensure that your SHSH is stored by Cydia. iSHSHit can also email your SHSH blobs to you for more permanent storage.
You must have jailbroken iPhone or iPod touch to install it. Follow our step by step guide posted here to jailbreak your iPhone, iPad or iPod touch with Redsn0w on iOS 4.2.1