• iPhone 4
• iPhone 3GS
• iPod Touch 4
• iPod Touch 3G
Download the program from http://www.limera1n.com/. It will look like this:

Then, just plug in your device, and click make it ra1n. It will then tell you how to put your device in DFU mode and once your device turns back on, you will have the limera1n app and you will be able to dowload Cydia there.