Rusty definately consider NI and perhaps Donegal in the north west. These two websites will give you some good ideas.
http://www.cycleni.com/national-cycle-network/
http://www.walkni.com/ulsterway/
I’d consider maybe making your way to Fermanagh, then into Donegal for a few days, Derry and then the North Antrim coast back to Belfast. Stops in Bushmills (distillery and Giants Causeway),Rathlin Island (good bird watching) then the Glens of Antrim before Belfast.
Plenty of opportunity for pubs, live music and awesome scenery along the way. I live over here so feel free to emial, in profile, if you want more info.