i probably own 15-20 putters.

i've always been partial to "center mount putters"...meaning the shaft of the putter is in the center of the putter head and doesn't have any offset.

ironically, the putter i've used for the last 7 years is one i won...it's a SeeMore putter. it was made famous by payne stewart when he won his US open. a few pros still use it, like zach johnson. i like it because it has a "alignment feature" that aligns the putter head as you look down the shaft with two white lines and a red line. if you can see any "red" as you look down, your head isn't square.

SeeMore became recognized when Payne Stewart won the 1999 U.S. Open playing a SeeMore putter. Stewart one-putted the last three holes to win the championship by one stroke. He sunk what's considered to be the longest putt in Open history on the 18th hole to win the tournament. Stewart also won the overall putting title for fewest putts per round over the entire 1999 season.

The SeeMore brand was re-launched with the new mSeries of putters in 2007 and immediately gained worldwide prominence again as Zach Johnson used a SeeMore FGP to win the 2007 Masters. SeeMore also is the putter of choice for the tour's best putter among the top 50 on the money list in 2006, Vaughn Taylor.
http://www.worldgolf.com/newswire/browse/9445-SeeMore-Putter-reports-seven-pros-using-their-putters-on-Tour