Actually vibrate only is still on the phone. Just use the volume down button and turn your ringer all the way down to get into vibrate only. The option that has disappeared in 2.2 is the silent mode option. In order to turn your phone on completely silent with no vibrate go into vibrate only mode and then turn off vibrate in the phone settings.
This actually was one of the few things I really didn't like about 2.2. I never use silent mode but it's nice to know that it's there if you need it.