3. Alec Baldwin
Alec Baldwin has become a reliable character actor over the years and has experience playing aggressive authority figures in films like The Departed and The Cooler, as well the Television series 30 Rock. His work on that show, as well as on Saturday Night Live, shows his comedic range as well, which would be an asset for his transformation in to the Green Goblin. I can imagine Baldwin would have no problem being sinister and funny as the Goblin, if maybe a little old to play the part.