The few times I have run into this I just stand in the exit blocking the other party from getting on and not saying a word... kind of a jerk move, but I guess I always excuse myself when I forget that there may be people trying to get off and I'm not paying attention.

Another item I have noticed...

Allowing women on/off the elevator first... that's old school etiquette, but I practice it. I didn't know that was one of the rules till a co-worker set me straight a couple years ago.

Non-etiquette, but common sense... taking the stairs if you are on the 2nd floor. I always laugh to myself when I see someone who looks like they've been waiting 10 minutes get on at the 2nd floor headed to the 1st floor. Not someone with luggage in tow, just someone who couldn't figure out that it takes 30 seconds to use the stairs.