There haven't been any American pilots to make the status of "ace" since the Vietnam War. One F-15 pilot did score two MiG kills in ODS and his plane scored three (his two and the third scored by another pilot), but that's been the most scored by an American since 1975.
There were no A/A engagements in OIF to my knowledge. The Iraqi Air Force sat this one out. Some of there MiG-25s even "buried their heads in the sand!"
Off the top of my head, Steve Ritchie and Randy Cunningham come to mind as Vietnam era aces, but I know there had to be more. Neither is no longer in the service but Ritchie still flies an F-4D at airshows. If you have the chance to see him, by all means go! I doubt there are any aces flying these days