iPhone Dev Team immediately responds Apple iOS 6 beta with a new special version of redsn0w specifically dedicated to iOS 6 beta release. Here you go with redsn0w 0.9.13dev3, tethered jailbreak for iOS 6 beta 3. This release is compatible with older devices like iPhone 4, iPhone 3G and iPod touch 4G.
Beware though, unlike the previous Redsn0w, this release does not automatically go to install Cydia, leaving the start and tweak tools, methods a little more "geeks", then via SSH or afc2. Naturally, this "lack" can be bypassed by installing Cydia at a later time.