The problem with this is that opinions change with time, as more and more fans who never saw some of these guys play come into the fold, and older fans mellow (or die off).
On the whole, the fan base seems to think much more highly today of Taliek than when he was playing, for instance. He was always a good point guard and a ferocious competitor. But few appreciated him for that in situ.
Donyell was exciting and loved as a Husky, but his less dominating performance in the league has tarnished his rep, as the memories of his college greatness grow older, and the percentage of the fan base that is too young to remember his husky career grows.
In my mind, the most underappreciated Husky ever was Ricky. Like Taliek, he was often criticized during his career. He was arguably (convincingly, in my mind) the MVP of the 99 championship. And his greatness has simply slipped from the collective memory of the fanbase over the last couple decades.
Then again, maybe I just value defense more than most, because my next choice for "underappreciated husky" would be Lyman DePriest.