The Dev-Team has updated redsn0w to work with the latest iOS 5 beta 4.
Note that this is a tethered jailbreak meaning you will need to connect your computer to your iDevice via USB on every reboot in order for it to be in a jailbroken state. From the Dev-Team :
Update #4: In conjunction with iOS5 beta4 being released to iOS developers, redsn0w 0.9.8b4 is now available for jailbreak app developers (point the b4 redsn0w at the b4 IPSW). Remember, it’s a tethered jailbreak right now so you’ll need to use redsn0w to boot into a jailbroken state at each power cycle.
NOTE: It appears that by design, the OTA update that became available starting with iOS 5 beta4 will *not* be automatically applied to jailbroken devices. That’s a relief to those who don’t want to lose their jailbreak via OTA pushes. If you’re jailbroken, you’ll need to use the standard iTunes method to get to iOS 5 beta4.