Funny... people rank 10 cornerbacks play, but have you actually watched them?
Given that you can barely see them on TV and how they all play for different teams, you must be some kind of fan.
Some of the staff members do game summaries and thus may watch a game more closely or more than once.

I don't see every game each week but will often watch 6-7 with particular attention to the defensive side of the ball. While it's not coaches game tape, things like recovery speed, ball skills, footwork, hands, and most frequent type of coverage played (press vs zone) among others can be gleaned from the telecast and some isolated replays.
Granted, I don't get to see many Texan or Niner games because of regional issues. So, some of the evaluation process is based on other scouting reports that you trust, reaction from defensive coordinators and opposing players (sometimes taken with a grain of salt), and an educated read of gamebooks and statlines.
So I guess you could say some of us are different kinds of fans.
So uhm from your

seat who are your top 10?
I piled on some thoughts last night in a reply to Aaron's list, which I thought was pretty good.Corner by nature is a very volatile position and confidence plays a huge role so some of these guys, while down a bit right now, still deserve to be in the discussion. I'm a tier rather than raw number rank kind of guy and here's how I see them. Just one guy's opinion.
Veterans at the top of their game
Champ Bailey
Leigh Bodden -- Very good and very underrated. Injuries have kept him from getting the love he deserves.
Rashean Mathis
Patrick Surtain
Terence Newman
Shawn Springs
Ronde Barber -- All he does is make plays.
Solid veterans (with issues)
Chris McAllister -- Gets beat deep entirely too often but still a solid press corner.
Nick Harper -- Not the best man corner but has really picked up his play in the zone Tampa-2 scheme. Having a great year.
Charles Tillman -- Tillman was at fault on maybe one of the Steve Smith plays. He wouldn't fit in an aggressive defense that required a lot of press coverage, but he's an excellent zone guy with tremendous ball instincts.
Al Harris -- Awesome in 2005, meh in 2006.
Antoine Winfield -- Can beat him deep, but I'd take his steady, overall play over a Dunta Robinson or DeAngelo Hall
Walt Harris -- Not as good as he's played this year but still pretty good.
Great skill sets but questionable play in 2006
Nate Clements -- Like Jekyll and Hyde this year in coverage and his tackling has been atrocious.
Chris Gamble -- See Clements, Nate.
Ken Lucas -- See....sorry, you get the point.
Up and Comers
Nmamdi Asamougha -- If this guy could catch, he'd be leading the league in picks. Of course, then he'd probably be a WR.
Pacman Jones -- He may be a butthead, but he's proving he can play with the best.
Overrated
Dunta Robinson -- Potential is there but he's too inconsistent.
Asante Samuel -- I'm with Bloom. Belichick gets the best out of nothing and having Rexy throw you a few ducks on primetime TV may get him bucks. See also: Brian Russell.
Deshea Townsend/Lito Sheppard -- Either could belong in the first category too but I can't shake the impression that they are average players made better by an aggressive front seven.
Quentin Jammer -- meh.
DeAngelo Hall -- Too much gamble. Much more likely to give up a big play than make one.
Shawntae Spencer -- Go back and forth on this guy, still too inconsistent for my liking.
Deltha O'Neal -- He's not as bad as the Broncos thought he was, but last year was a fluke.
Rookies with potential
Johnathan Joseph -- If he had any kind of hands at all he'd be getting just as much talk as...
Richard Marshall -- Tough man-to-man proving to be really physical in run support.
Antonio Cromartie/Tye Hill -- Two totally different players who could grow into very good man cover guys.