I kept this to skill position mostly because, while linemen can be both very good and very underrated, they naturally are talked about less, on average, than the the guys in the "vanity" positions. We can do one with linemen next.
I'm 32 so have been following the Buckeyes since I can remember, but the '95-'96 seasons are the ones I can first vividly remember.
Some of our skill position guys that I'd put in the "most underrated" category I can remember are:
Brandon Saine - never going to be an all star but at a time when we needed a back like him he did a pretty good job.
Dane Sanzenbacher - not underrated in terms of his accomplishments: All-American, All-Big Ten, etc but nobody really talks about him much when talking about great OSU receivers and he really was great. In an offense like we have today he'd be the guy annoying the HELL out of defensive coordinators.