Galway; As Jim says - start at the Crane Bar on Sea Road. Get to Kinvara (about 20 km away) if you can.

Inishmore: Dunno! Pretty tourist-oriented in general. This increases your chances of getting SOME music - but does little for your chance of GOOD music! The main village (Kilronan) is very small so, if it's there, you'll find it. The two smaller islands (Inisheer and Inishmaan, in English) have more of a reputation for sessions, but would still be hit and miss. Ask in the tourist office.

Letterfrack: no idea!

Dublin: the Goilin starts on the first Friday of September. The Cle Club is, I think, out of action at the moment. Hughes's and The Cobblestone are the best starting points.

Regards