So many great musicmakers mentioned here but I didn't see any mention of the Sligo band, Dervish. The bouzouki/mandola interplay alone is worth the ticket but I think they're a great band top to bottom. Maybe some trad folks take them less seriously because of their involvement in Eurovision. I don't know.

The American/Irish band Cherish the Ladies is also worth a mention especially when they're performing traditional tunes and songs. My favorite recordings- "The Girls Won't Leave the Boys Alone" and "Women of the House" both of which are pretty song-heavy. The leader Joannie Madden, flute and whistle, is to me one of the finest musicians on the planet.

Andy Irvine's received mention here but it's worth reiterating that everything he's been involved with, including Sweeny's Men, Planxty, Paul Brady, De Dannan (briefly), Patrick Steet and Mozaik has been world-class.
I see that he and Brady are performing at Vicar Street today as part of a 40th anniversary of their landmark album tour with Donal Lunny and Kevin Burke who played on the original recording.