For me, there are a few:

Damon Arnette being drafted in the first round by the Raiders genuinely had me shocked. In hindsight, only AJ Terrell was a first round worthy CB actually taken in the first round that year, but still. 

Haskell Garrett going undrafted still makes no sense to me. He wasnt an elite player necessarily but was productive, showed a lot of resolve throughout his career, and had good athleticism with size. 

Carlos Hyde not being the first RB taken in his class. Bishop Sankey and Jeremy Hill over Hyde, really?