O2 Ireland have had a micro-sim for iPad available since May 28th.

It's available from O2 stores and is nominally free, although you are required to purchase €20 credit at the time of purchase. No ID required iirc.

Packages are both pre-pay, €3.95 daily (500mb). €19.90 30 day validity (5Gb)

Top up online.

APN: open.internet
Username: gprs
Password: gprs