At the moment I buy:
Hellboy, B.P.R.D. Fantastic Four (but only whilel Bryan Hitch and Mark Millar are doing it), Buffy. I buy non regular stuff as well such as Sin City, Wanted or more recently Allstar Superman for example.
I also buy anything (has to be the full comic not just covers) drawn by Glen Fabry, Brian Bolland, Frank Cho, Arthur Adams, Alan Davis, Adam Hughes, Alex Ross, Mike Mignola, Frank Quietly.
On average I maybe buy 5 or 6 comics a month?