One Earth:
Spider-Man/Peter Parker: Anton Yelchin
He was good enough for All-Star Spider-Man, and dammit, he's good enough for OE Spidey!
Gwen Stacy: Imogen Poots
She's got the 'sweet, wholesome girl next door' look that I see in OE Gwen, and is a pretty decent actress to pull it off.
Harry Osborn: David Franco
I liked James Franco as Harry back in the Raimi movies, so since we're making Spidey younger again, why not use his little brother? Besides, Franco the Lesser was pretty damn entertaining in 21 Jump Street, and I can see OE Harry very much like the character he played in that.
Mary Jane Watson: Emma Stone
I know she's playing Gwen in the new movie, but I've said it before and I'll say it again, Emma Stone was
born to play MJ. This is kinda cheating, since MJ hasn't actually showed up in OE yet, but she's coming.
Uncle Ben: Kurtwood Smith
He wouldn't be as much of a total hardass as he was in That 70s Show, but I definitely see Uncle Ben in the same type of old-fashioned, blue-collar father figure role. Plus having a more gruff nature to him makes it more touching when he does let his guard down, rather than if he's always a touchy-feely kinda guy.
Aunt May: Sally Field
Eh, I like the casting choice for
Amazing Spider-Man. Sue me.
Norman Osborn: Ralph Fiennes
One of the all-time great villain actors, a guy who can be classy and sleazy and terrifying at the drop of a hat.
Speaking of villains......
The Joker: David Tennant
Provided he can do an American accent, Tennant could be an amazing Joker, being able to pull off his over-the-top theatrics, his run on Doctor Who giving him an air of being incredibly intelligent and still undeniably crazy. He's a phenomenal actor, and is already skinny and hawk-faced enough to play Mr. J.
Dr. Jeremiah Arkham: Jackie Earle Haley
Arkham Asylum is a creepy place, so it makes sense that it should be run by a suitably creepy guy.
Jonathan Crane: Tim Roth
Roth was just born to play a supervillain, and I think he'd be a fantastic Scarecrow.