In terms of tennis quality the way he has played against Hewitt this year has been amazing. I don't know if it is because of a favourable match up but Federer has just raised his level so much every time he has played him.
Memorable wins this year apart from the Hewitt ones:
Beating Nalbandian at AO (you sort of knew he would win the title after he got through that one)
Beating Henman at IW (his last nemesis)
Beating Coria at Hamburg (ending that streak on his worst surface against a guy who looked unbeatable up until that stage)
Beating Roddick at Toronto (on Roddicks best surface with Roddick in terrific form)
Beating Agassi at USO (so many things going against him and that 5th set
Beating the inform Safin at the masters especially the way Safin played in that second set
For mine Rogers best victory was in the Wimbledon final. Many felt Federer was always in control but for me there were 3 or 4 points in the match where Roddick was playing the best I ever seen him play and on the verge of really taking control of the match but Roger hanged in there and when he won with that ace it was definetly my happiest Roger memory of 2004.