Hi RaBa. Here are a few links:

Irish Mudcatters? - a recent Mudcat thread

Inishowen Seminar (been and gone for this year, but site has some useful contacts)

Irish sessions: Where do you play? Another Mudcat thread (note that some of the contributions here were posted a while ago)

Irish Music Magazine - lists sessions, festivals etc

Any folk clubs in or around Belfast? - another Mudcat thread

Comhaltas Ceoltóirí Éireann - organise fleadhs around the counties and provinces, including Fleadh Cheoil na hÉireann (the all-Ireland) which will be in Listowel this year (details here).

I'll be surprised if I haven't screwed up the html somewhere in all this...