Usually, a microfiber cloth; but sometimes, I dip the tip of a Q-Tip in Windex and wipe the screen and let it dry naturally. With that said, I've only done this to clean the screen protectors - I've never not used a screen protector : )
I use the glass cleaner, just keep cleaning it every night. I don't see any smudge leave on the surface that's hard to clean. I think a routine clean is just enough for me.
I've always just breathed on mine to create a little fog on the glass, then use a microfiber cloth to wipe the screen. Works beautifully, with no chemical residue or anything else.
I use a spray gel electronic screen cleaner and a micro fiber cloth. Works good. I wouldn't use a cloth I carried in my pocket myself though, they can collect grit and easily scratch screen
I think the heavy breathers and alkies have it right, along with a clean microfiber lens cloth.
I've read that a good exhale onto the screen creates a weak fog of carbonic acid that is best for cleaning glass. In fact, we have very expensive birding binoculars and both manufacturers recommend using only this method for cleaning.
I also use a weak isopropyl alcohol solution occasionally for tough smudges.
I found I had a about 2 dozen of these LCD wipes that come in little packages that look like KFC wetnaps. They are semi-wet and seem to do a pretty good job. Though I may still buy the ZAGG foam once I'm out of these.