According to AICN and a growing amount of "chatter" on the web, Thomas Hayden Church's bad-guy role in "Spider-Man 3" may indeed be... The Sandman.
There's a pretty decent writeup of his history (and some good Official Handbook-style character images) to be found HERE...
...but as you might guess, the basic idea is that the guy is made of sand.
First reaction: I'm still just glad it's NOT Carnage.
Second reaction: This is actually an interesting choice. Sandman (aka Flint Marko, aka William Baker) is one of those fun sort of "second-tier" comic baddies who's called a Spidey villian because thats where he originated but has come to be more of a perennial Marvel Universe "jobber" who wound up in scuffles with almost every costumed hero at one time or another, mostly because (as already stated) he's made of sand, which is kind of automatically cool and must be a lot of fun to write and draw.
Thus, what we (apparently, since no one from Sony or Marvel can confirm this) might have here is a main baddie who's essentially always been a "hired thug" character, (though last I checked he'd reformed and become a good guy,) short on pyschology or complexity. So, then, what's his function in the film? Retooled into a more potent threat? A hired-thug used by Harry Osborne? It'd certainly make sense if he was only ONE of two or more bad guys, being more of a "grunt" than the big-picture-oriented Green Goblin or Dr. Octopus, which would lend tantalizing credence to all those rumors about Chloe Sevigny and The Black Cat awhile back...
I live for this stuff.