Fairly arbitrary and not necessarily based solely on sheer quality, but two of my favorites have always been Cocu and Laudrup.
Cocu was never our best player, but he was so versatile and 100% dependable. A true leader and class personified.
As a Dane the Laudrup pick is a no-brainer. One of the most graceful players in the game ever. The unspeakable move obviously tainted his legacy, but I've learned to forgive him with time and directed most of my animosity regarding the transfer towards Cruyff.
Petit and Overmars?! I mean, Overmars was not a total bust (very close though), but Petit was shockingly bad - especially so when you consider the fee we forked out for him.