I was also thinking asparagus ferns, or maybe some Wave petunias (I just got the seeds in the mail!).
I'm also considering Euphorbia Diamond Frost. It did unbelievably well last year in our intense heat and humidity!
Karen, there is a drainage hole, but it sits right on top of the saucer. I'm going to put water bottle caps underneath, so there's space between the cup and the saucer.
Hmm... this is probably a good tip for the "Tip of the Day" section!