I had my done here:
The Genographic Project (Have Your DNA Checked, Find Your Roots
Because of blam, and only because of blam (his posts on the subject over the years), I had my DNA done at The Genographic Project last year. Paternally, I'm haplogroup I1a (now same as I1). Maternally, I'm haplogroup H. My paternal sequence has the M253 marker, which means that my male ancestor arrived in Britain with the Anglo-Saxons, or later with the Vikings. There isn't enough resolution with the Genographic's 12 STRs (short tandem repeats) to be more exact.
Those with haplogroup I are fortunate to have a good mailing list, and Dr. Ken Nordtvedt:
Y-DNA-HAPLOGROUP-I-L Archives
Index of /~knordtvedt