Shortly after the announcement at WWDC, Apple leaked iOS 4 GM to Developers. We had soon discovered that redsn0w 0.9.5 had the ability to jailbreak the newest release candidate, however, there were some issues with this process and not all features were fully functional.
The Dev-Team has released redsn0w 0.9.5b which has been updated to be more compatible with iOS 4 GM. Multitasking and Wallpapers are now functional on the 2G with this release, which is two of the main features many of us are looking forward to in iOS4, although we were afraid we might not get these features for older models.
The redsn0w beta has been updated for 4.0GM, and it now supports the iPod touch 2G too. Multitasking and homescreen wallpaper are now turned on by default (Apple doesn't normally allow this on these 2 devices). (Update: the 0.9.5b5-1 version now lets you decide whether you want multitasking and wallpaper enabled or not.)
Download Redsn0w 0.9.5b