Via Buddy TV, here's a whacked out theory that's apparently been around for half a year or so: HEMA Theory. I haven't had the time to read through the whole thing in detail, but two things stand out to me here:
1) The guy knows his Lost details
2) My gut reaction is that he's crazy
Now maybe that will change when I've read through everything. His basic theory seems to be that the island amplifies psychic energy into whatever the person desires (i.e. The Magic Box) and does so through special magnetic properties found in the rocks on the island. That's why the Others wanted Walt and that's how Locke's dad ended up on the island.
That's actually sounds pretty plausible given what we know and the guy certainly knows his details. But it's awfully hard to read because for every coherent thing he writes, there's a paragraph of psychobabble, like something L. Ron Hubbard would come up with.
I haven't gotten to his theory on the Monster yet, but I'm curious. Take a look and tell me what you think.