Whenever you are speaking at an event where food is being served at round tables, you can use the centerpiece area as part of your program. I recently saw Dr. Shirley Garrett do this at large keynote speech. She was using juggling scarves on stage. The centerpiece of each table was draped in these scarves. It looked great, it was inexpensive, it related to her presentation, and it gave each attendee something to take home to make it easier to remember her message. This idea could also score you some points with the meeting planner who may be able save quite a bit of money on flowers or other ornamental centerpiece items.
In addition, this area of the table could be used as revenue generator for you. I cover this in tape six of the "Wake em Up Video Professional Speaking System" http://www.antion.com/speakervideo.htm You pre-sell your books or tapes to the meeting planner and stack them attractively in the middle of the table. This gives everyone at the table something to take home and won't cost much more than a fancy centerpiece that only one person at each table gets as a door prize.
Use the middle of a round table to tie your message in AND make more money.