What is the best way to use two 27" monitors on your desk? In my work environment I have three smaller monitors and love the productivity benefit. At home I have two 27" displays (the iMac and an external cinema display), but am having trouble laying them out on my desk so I can effectively use them without neck strain. What's the best layout for ensuring most of your work involves you staring straight ahead at your work, while still letting your work spread out over all those lovely millions of pixels?

EDIT: responses so far have focused on having the monitors at the right level, i.e. at and below eye level. But the problem I'm having is that just one monitor nearly fills my field of vision, so I end up turning my neck or chair dramatically to work on the other.
You don't say what you'll be using them for.  I'm (among other things) a programmer, and for me being able to see a tall vertical area in my text editor is of primary importance.  Thus, given 2 widescreen monitors, I'd set them up vertically, next to each other.

I'm not unique here: when I visited Google, most of the programmers I saw had this layout too.

I would think this could help with your neck problem, since it makes the display area closer to a square, and not a really wide rectangle.  Alternatively, you could keep them horizontal, and stack one right above the other.  Depends on the shape of the things you're going to be looking at most, I guess!