Amazing Villains
David Tennant - Mysterio/Quentin Beck
I casted him in my other Spider-Man fan cast and I think this is the perfect Marvel character for him.
Gerard Butler - Kraven the Hunter/Sergei Kravinoff
I know it's not very original, but Gerard Butler is prefect for this role.
Vinnie Jones - Juggernaut/Cain Marko
2 reasons for this casting, 1. I thought he was awesome in X3 and 2. I've always imagined the Marvel movies as one big universe itself too bad it's not.
Thomas Haden Church - Sandman/Flint Marko
For continuity's sake.
Ultimate Villains
Dane Cook - Ultimate Deadpool/Wadey Wilson
Since Ryan Reynolds would my choice for classic Deadpool, Dane Cook would be awesome as Ultimate Deadpool.
Michael Rosenbaum - Ultimate Electro/Max Dillon
He looks like Ultimate Electro and is an awesome actor.
Noir Villains
Harvey Keitel - Noir Hammerhead
I think this is a really perect fit.
John Malkovich - Noir Vulture/Adrian Toomes
He's my second choice to play Vulture in an actual Spider-Man film, so I decided he be great for Noir Vulture.
2099 Villains
Emanuelle Chriqui - Doctor Octopus 2099/Serena Patel
I think she's a pretty decent actress so I think she'd be great.