I've got my eyes *just* above the top of my monitor. It actually feels like my eyes are quite a bit lower, the only reason I realized this is because I have a mirror behind my monitor that I can see my eyes in.
Monitor slightly tilted up, to get closer to perpendicular angle of vision to the center of the screen.
Some good links about ergonomics, including monitors:
Microsoft US Department of Labour ErgoCanada (I realize this site doesn't look great, but their info is good, and they're a Canadian company that I've had fantastic experiences with.)