Shutter button / AE lock button

[maccaroneski]

Assuming that is what your camera allows! (Another reason to upgrade)

On my d40x, I set the AE/AF-lock button to be Focus, and then the shutter button becomes AE-lock (half) and shutter(full). This is the closest I can get to I@M's ideal. (Unfortunately, the AE/AF-lock doubles as "lock photo" when you are looking at the shots. If (when!) I chimp, I have to be careful when I go to take another shot. I always end up with about 10 photos "locked" on the card!

Same for me - the D90 only has one the one AE/AF button, so I use the half press of the shutter button as the AE lock.

[RaoulIsidro]

I use #1 most of the time, except for studio, landscapes and interiors where I go full manual.