First, I googled 'Fallout New Vegas voice actors' and didn't come up with Liam O'Brien on wiki or IMDB (actually, both lists are kind of short). I checked the game guide. I checked the game insert. I was at a loss.
In desperation I started the credits rolling and, eventually, THERE IT WAS. With lots more names-with-characters than Wiki or IMDB bothered with, I might add. But there was the name 'Liam O'Brien' poor, doomed Niall from Dragon Age, or suspiciously strange Victor Law from Ergo Proxy. Or even one of the voices of Illidan Stormrage from WoW (still not quite believing that one)
At this rate, I will be recognizing his voice anywhere.
Maybe I can sleep now....
*Didn't hurt that I kept hearing it. I am thinking he did most of the male voices for the NCR.