One of the best tattoo artists in the U.S., IMO, is Paul Booth. His work is some of the most evil shit you'll ever see. His shop (Last Rites) has a web site...check him out. I understand that he has one hell of a waiting list to get an appointment though. I have a couple of pieces that were designed by him, but I have yet been able to get one inked by him. I will make the necessary journey one of these days...one way or another.
Here's the link to his web site;
http://www.darkimages.com/enter.asp