Jailbreaking is the process by which an iPhone firmware is modified to allow unsigned code to be run to gain access to files that Apple wouldn’t normally let you access. Jailbreaking adds unofficial application installers to your iPhone such as Cydia or Icy (I personally only use Cydia), which let you download many 3rd-party applications previously unavailable through the App Store.

This page is a reference guide to the latest iPhone jailbreak methods available. Simply look for the firmware version you want to jailbreak and the type of iPhone or iPod Touch you have, then click on the link to see a detailed tutorial on how to jailbreak your iPhone or iPod Touch.

Firmware 3.1 Jailbreak

Jailbreak iPhone 3GS

• Not Available Yet – Check back here later.

Jailbreak iPhone 3G

• Jailbreak iPhone 3G 3.1 using PwnageTool for Mac OS X

Jailbreak iPhone 2G

• Jailbreak iPhone 2G 3.1 with PwnageTool for Mac OS X

Firmware 3.0.1 Jailbreak

Jailbreak iPhone 3GS

• RedSn0w tutorial

Jailbreak iPhone 3G

• RedSn0w tutorial

Jailbreak iPhone 2G

• RedSn0w tutorial

Firmware 3.0 Jailbreak

Jailbreak iPhone 3GS

• RedSn0w tutorial (recommended)
• PurpleRa1n tutorial

Jailbreak iPhone 3G

• PwnageTool for Mac tutorial
• RedSn0w for PC and Mac tutorial

Jailbreak iPhone 2G

• PwnageTool jailbreak tutorial for Mac
• RedSn0w tutorial for Windows and Mac

Jailbreak iPod & iPod Touch 2G

• RedSn0w tutorial

Source: iPhone Download Blog

If you are Jailbroken, or considering a Jailbreak, there is very rarely a better source for all the latest information on Jailbreak, Unlocking, new Jailbreaks for new firmwares, and so on.

The iPhone Dev-Team Blog (Jailbreaking)

The iPhone Dev-Team Tweets (Jailbreaking)