Marilee, welcome, and thanks for the kind words.
Toward the end of each month, I choose the 4 or 5 pieces that will be showcased for the following month. I have several different ways that I find pieces. I have a list of the 500, and I can click anyone's name and read through their postings. I also look through the "newest regular postings" for the little "500" symbol, and read those. If there's a particular holiday coming up, I may solicit writings on that theme here on the message boards, or I may search for particular keywords using the "search" function.
I try not to use anyone more than once a year or so, as there are so many people in the 500. And recently, I've been noting new members and showcasing them.
The pieces may be challenge articles, regular submissions, or free reprint articles. If its a challenge article and it needs a tweak or two, I may PM the member and ask them to put it in regular submissions with a few edits.
Hope this answers your questions! I've got February done, but if you have something you'd like me to consider for March, let me know.
That goes for all of you 500 members, new and old--if I haven't showcased you for a while, drop me a PM or an e-mail.