I picked up a copy of The Grand 2, which is supposed to run just fine on Intel Macs and with Logic 8, but even after installing it, authorizing it, and making sure that the plugins are in the right place, it won't turn up in Logic's AU Manager or in the AU dropdowns in an individual track.
I tried trashing the com.audiounits cache file, that didn't do anything. Also took the AU out of the AU folder and started Logic, quit logic, reboot, then put the AU back into the AU folder and restarted Logic hoping that that would force an authorization, but no such luck. Repaired permissions, etc, as well.
I've sent a tech support request to Steinberg, but from what I've heard/read about them I shouldn't exactly sit around and wait for the phone to ring! If you've had this problem yourself, please let me know how you fixed it! I'm out of ideas.