The Bar part of the Trinity Rooms has a good selection maybe a dozen types of bottled beers - Duval, Schofferhoffer etc. Other than that it is hard to find good beer in Limerick city.
Out towards Killaloe is Tara's Bar, which has an awesome selection, first thing you notice when you go in is the blackboard on a wall with all the types of bottled beer available(into the 100s). But would probably involve needing a lift or driving.