I was wondering what peopple's opinion's or experiences in this area are. This should not be your first criteria to go with 3-tier. If you have only a few client users, you may not need that headache.
Tuxedo is the middle tier.
Tuxedo has RPC like functions. It is request-reply mode. Tuxedo also provide a conversation mode, if you need it. You may consider using Java as your first tier. In this way, your middle tier will be very thin.