Underrated players at United for me:
Antonio Valencia: very good as a winger, excellent as a right back, but some seem to be upset that he wasn't as good as Ronaldo and couldn't cross like Beckham.
Carrick: the fact that many in this thread are trying to argue he was 'alright'. He didn't have flair, he wasn't all action (in fact he was rather languid), he didn't shout and point, and he didn't maraud forward to score goals, so its easy to miss what he did. His positioning and reading of the game were second to none, he was at the right place at the right time and coupled with his excellent passing range made controlling the midfield look easy.
Scholes: rated as he should be by the majority of our fans, but underrated by oppo fans usually. I mention him because I had an argument on here with a united fan who thinks Patrick Vieira was a better midfielder.
John O'Shea: probably one of the most complete players ever. While never the best in any one position, he has played every position on the pitch from goal keeper to striker (and everything in between) for us at a very high level. Was quality as a CB after leaving united.