Use Sainsburys website as a rough guide as most stores seem to stock quite a lot of other stuff which isn't listed. Also not everything listed on the website will be available in all stores (sadly most stores i've been to recently have stopped stocking the Meantime brews)...
One that's worth picking up and which seems to be available in most stores is Weihenstephaner Hefeweissbier Dunkel - very tasty
The Whitewater brews are widely available - usually Clotworthy Dobbin and Belfast Ale. The Belfast Lager less so...
Guiness Foreign Extra and Timothy Taylor Landlord are always available and are always worth picking up...
As TheBeerNut said the Vineyard is a must if in Belfast. Also GapWines (<!-- m --><a class="postlink" href="
www.gapwines.com/">
www.gapwines.com/) is well worth a visit. The Website currently lists Brooklyn Black Chocolate Stout and also the Brown Ale - sadly neither of these are in stock at the minute (i think i cleared them out when they were !!)