Whitewater is the one near me! :) you can get their bottled beers in tesco and a couple of other supermarkets. i love the Clotworthy Dobbin, but it blows my head off if i drink it all night. the Belfast black is quite good too. i think there are some pubs up around Lisburn and Belfast that have them on draught, but i've never been to any. i'm intrigued by this signature beer 8)
haven't tried Strangford, but i'll have a look for it