My "surprise" Pokemon coming through HG is the Machamp line. It's not that I thought that evolutionary line was weak, it was really the entire fighting type. The only fighting type I've ever used since I started playing Blue 8 years ago was Lucario in Platinum and he didn't really do anything either. I rarely used him to beat anything so he lagged a few levels behind the rest of the team. When I got to the Elite 4, he came out for one pokemon and only as a sacrifice so I could revive/heal. He basically reassured my assumption that despite doing super effective damage on 5 types and being weak to only two, Fighting sucked.
That was until I traded a Drowzee (who was pretty beast himself) for Machop in Goldenrod. Muscle is a Machamp now and he is a one man wrecking machine.