If you're into going to a few pubs, regardless of the beer, (they all pretty much have the same) I'd go for
The Long Hall, The Stags Head, The Oval, Smyths or Sin E.
If you're in Temple Bar, I'd say The Temple is the best bet, (it's been a while since I've been though).
I wouldn't rule out a visit to the Guinness Storehouse, it's the tourist attraction part of the Guinness Brewery, I thought it worth the price, even if you don't get within an ass's roar of any real brewing.
As stated above, the Porterhouse, Messers Maguire, the Bull and Castle or the Gingerman are your only real bets for beers that aren't the usual global brands. Which personally I think is slightly tragic.