20. Daunte Culpepper
Culpepper had a good NFL career but it could have been brilliant. Unfortunately, a major injury stalled his prospects after his best season. It looked like he was finally developing into a top-tier passer. The three-time Pro Bowl selection led the league in passing yards in 2004. Then, he damaged his major knee ligaments and it all went downhill.
The All-Pro never recovered properly. He drifted from Miami to Oakland before retiring with the Detroit Lions. Culpepper spent most of the final five seasons as a backup. However, he was very effective at his best for the Vikings. Minnesota fans remember him fondly albeit with some frustration because of his stunted potential. He threw for over 4,700 yards in his best season with 39 touchdowns (via The Undefeated).