I have to admit I usually end my PA with "...sit back, relax and enjoy the flight with us this evening". It usually seems like an good ending to the spiel, now I can't think what else to say to round it off!
In my company its always the Captain that does the welcome PA and the PF does the inflight PA's. The pax always like to hear the Captain's voice but it seems more sensible for the PF to say where we are, where we are routing, and then to thank them at the end. And its good practice for when moving across to the LHS!