Popular tethering app MyWi recently received an update that adds compatibility for iOS 5. f you don't currently own MyWi you can install a trial via Cydia. You'll have 3 days to test it out in demo mode. After that you can purchase MyWi for a one time purchase of $19.99 when the trial expires.
It's worth noting that carriers typically frown upon the use of unauthorized tethering apps. Some have even taken matters into their own hands. So if you're an extremely heavy data user, you'd probably be better off just adding a tethering plan through your carrier.