Here's a list I have compiled, with the alternate number listed when known --
NFC Alternates
Quarterback -- Donovan McNabb (first), Kurt Warner (unknown), Eli Manning (fourth)
Running back -- Frank Gore (first), Ryan Grant (unknown)
Wide receiver -- Steve Smith NYG (first)
Tight end -- Brent Celek (second), Visanthe Shiancoe (unknown)
Tackle -- David Diehl (first), Levi Brown (unknown), Chad Clifton (unknown)
Guard -- Chris Snee (first), Davin Joseph (second or third), Carl Nicks (second or third), Todd Herremans (fourth)
Center -- Jonathan Goodwin (first), Jason Brown (third)
Defensive tackle -- Pat Williams (first), Justin Smith (second), Brodrick Bunkley (fourth)
Defensive end -- Will Smith (first), Andre Carter (second), Justin Tuck (third)
Outside linebacker -- Clay Matthews (first), Julian Peterson (unknown)
Inside linebacker -- London Fletcher (first alternate), Jon Beason (second), A.J. Hawk (unknown)
Cornerback -- Antoine Winfield (first), Sheldon Brown (second)
Safety -- Antrel Rolle (unknown), Roman Harper (unknown), Quintin Mikell (third), Antoine Bethea (unknown)
Kicker -- Ryan Longwell (first), Neil Rackers (unknown), Olindo Mare (unknown)
Punter -- Ben Graham (unknown), Donnie Jones (unknown), Jon Ryan (unknown)
Kick returner -- Percy Harvin (first), Johnny Knox (second), Domenik Hixon (third)
Special teamer -- Michael Robinson (second), Sean Morey (unknown)
AFC Alternates
Quarterback -- Ben Roethlisberger (first), Carson Palmer (third), Matt Schaub (unknown)
Running back -- Thomas Jones (first), Cedric Benson (second)
Fullback -- Ahmard Hall (first), Lousaka Polite (second), Vonta Leach (unknown)
Wide receiver -- Randy Moss (first), Chad Ochocinco (second), Vincent Jackson (third), Santonio Holmes (fourth)
Tight end -- Heath Miller (unknown), Zach Miller (unknown), Marcedes Lewis (unknown)
Tackle -- D’Brickashaw Ferguson (first), Michael Roos (second?), Marcus McNeill (third), Ryan Diem (fourth?)
Guard -- Ben Grubbs (first), Bobbie Williams (second), Chris Kemoeatu (fourth)
Center -- Kevin Mawae (first), Matt Birk (unknown)
Defensive end -- Shaun Ellis (second), Richard Seymour (unknown)
Defensive tackle -- Tony Brown (first), Domata Peko (second), Randy Starks (third), Kyle Williams (fourth)
Outside linebacker -- Keith Bulluck (first), Terrell Suggs (unknown), LaMarr Woodley (unknown)
Inside linebacker -- Bart Scott (first), David Harris (second), D.J. Williams (third or fourth)
Cornerback -- Johnathan Joseph (second), Antonio Cromartie (third), Leon Hall (fourth)
Safety -- Brandon Meriweather (first)
Punter -- Mike Scifres (third)
Kick returner -- Darren Sproles (first), Jacoby Jones (unknown)
Special teamer -- Montell Owens (first), Joshua Cribbs (second), Tom Zbikowski (unknown)
------------------------
Teams whose alternates have been reported -- Arizona, Baltimore, Chicago, Cincinnati, Green Bay, Houston, New Orleans, N.Y. Giants, N.Y. Jets, Oakland, Philadelphia, San Diego, San Francisco, St. Louis, Tampa Bay, Tennessee, Washington
Teams whose alternates are unknown or partly known -- Atlanta, Buffalo, Carolina, Cleveland, Dallas, Detroit, Denver, Indianapolis, Jacksonville, Kansas City, Miami, Minnesota, New England, Pittsburgh, Seattle