His voice is just wonderful, isn't it? I've recently just discovered his solo sean-nós work. His latest album is 'Invisible Fields' which I feel is even better than 'Seacht', partly because it uses more traditional instrumentation rather than the synthesizer background that seems to be on every song on 'Seacht'.
Iarla is on Real World Records, and his web site is here:
http://realworldrecords.com/iarla/ I highly recommend downloading "The Humming of the Bees (Aoibhinn Cronán)" from that web site, which is far superior to the version on 'Seacht' (again, the 'Seacht' version is way too synthesizer heavy).
In case you weren't aware, Iarla is the lead singer of Afro Celt Sound System, also on Real World Records:
http://realworldrecords.com/afrocelts/