ok, I suppose being one of the irish cavers on this I should reply
Clare's too far to travel to on a one-day pass. So you're stuck with Fermanagh.
Tullyhona Rising - be very careful of water levels.
Cascade Rising - a cracking trip. the entrances series is a bit of a sod (route finding is interesting), but beyond is very nice.
Marble Arch Cave - Normally need to contact the showcave (or other local contact to get a key) but access is closed at the moment. The show cave is putting in some new lighting and access to cave is denied until that work is complete (March?)
Prod's pot: Great SRT trip. mind the squeeze on the 5th! plenty to do once you reach the streamway.
Noons Hole: Again, mind the weather. The pitches can get very wet. As mentioned above finding the route to the Arch streamway is trickey.
Reyfad - No access. Don't even think of poaching it!
Poll na Gollum of the Boats - need to get permission. Contact a local caver for details. Mind the boulder chokes!
Poll na Raftra- need to get permission. Contact a local caver for details.
Give me a shout if you some contacts/ more details. When are you planning on going?
Dunc