4.0 - 4.0.2 Jailbreak!
Finally the iOS 4.0 jailbreak is here! Enjoy the multi-tasking enabled on any device you want, all the features of iOS 4.0 with the benefit of Cydia and Installous. This is the easiest jailbreak yet iPhone 4, iPhone 3GS, iPhone 3G, iPad, iPod Touch
This is the RedSn0w guide is for all devices except for iPhone 4, Windows or Mac.
3.1.3 Jailbreak!
I recommend at this point not to upgrade to 3.1.3 and keep your 3.1.2 jailbreak. It will only make things more complicated as not all devices are compatible, some of them can be jailbroken but not unlocked, it's all a bit confusing. There really isn't much new to 3.1.3. The update, which is available for download now, fixes a number of known bugs, patches known security issues, and improves various iPhone features. However, despite the good news for the majority of regular iPhone owners, the upgrade has posed something of a problem for those who have taken the notorious jailbreaking route, so please stay simple and keep your 3.1.2 jailbreak for now. If you accidently upgraded to 3.1.3 or something like that you can follow this jailbreak tutorial for Windows here or iPod Touch here. Mac guide here.
3.1.2 Jailbreak!
This was by far the easiest jailbreak I had ever done. It can jailbreak and unlock almost every device, in a matter of minutes! No entering DFU mode, restoring in iTunes, just click "Make it Rain", and in a matter of minutes your jailbroken. The is not much change from the previous update, just a few bug fixes. To jailbreak on Windows or Mac, follow this guide.
