"The Lee Sessions" will tell you everything you need to know about trad music in Cork. Very up to date as well. Sine in Cork is pretty good, but a but wild (sessions Tuesday, Friday, Sundays). Tuesdays have lots of tunes in D minor & F (great banjo and fiddle players run the session, but I can't really join in too much on flute). Fridays and Sundays also have the occasionally balkan or oldtime tune thrown in.

The Corner House (right next door to Sine) has sessions Tuesdays, Wednesdays and the first Friday of every month. Repertoire is more standard traditional tunes, except for on Fridays were loads of Sliabh Luachra music is played (about 40% slides and polkas).

Gables is also nice, but usually very quiet (2-3 musicians). Session on Wednesdays and Sunday nights.