Redsn0w 0.9.8b6 Takes Care Of iOS 5 Beta 6 http://snapvoip.blogspot.com/
iPhone Dev-Team has updated redsn0w to readsnow 0.9.8b6 to support Apple's newly released iOS5 Beta 6. Keep in mind if you are not a registered developer of Apple, this will be a exercise in vain and if you are a developer, remember this is a tethered jailbreak. Meaning every time your iDevice loses power or reboots, you need to jailbreak.
We’ve released redsn0w 0.9.8b6 to jailbreak iOS5 beta6 (point it directly at the beta6 IPSW). Two important notes about this version: (1) Please let your device boot normally to IOS5b6 and do a clean shutdown (slide to power off) before jailbreaking. (2) Boot logos have intentionally been disabled for now, so you’ll see a black screen on tethered boots (you can re-enable logos or verbose boot with command-line options if you really want them back).Dev-team via Geohot
Due increased sensitivity to abrupt filesystem shutdowns in IOS5b6, it’s very important that you do a clean shutdown before running redsn0w.