Beyond just using various sturdy materials under linens for height and pretty platters:
I’ve done glass vases for risers myself. I once saw a florist use floor vases on the table top. The arrangements were mostly greenery and a few birds of paradise, inside the vases she had koi fish swimming!!! I always thought that this could easily translate to the vase as the riser for a plate of something; I haven’t had an opportunity to do this. I tried to sell the idea to a bride and groom who were both marine biologist and using fish as the theme of their wedding. However, they leaned toward the idea that the use of live fish as decoration was some how inhumane. :) I do have a client lined up for a Mardi Gras Ball next year who really likes the idea. If it pans out, I’ll let you know.
A little labor intensive, but a neat effect, is using Styrofoam blocks, covered in foil or waxed paper, then a layer of greenery affixed with floral pins. Not just stuff from the produce section but washed yard clippings, magnolia leaves, ivy etc. (it’s free!) obviously make sure you don’t use poisonous plant material. You can build like legos (secure with dowels if you start heading toward the Tower of Babel) with “terraces” wherever you want. This is a great way to make a “tower” of cheeses, fruits or whatever with a slightly tropical motif. It looks really cool.
Even though it is labor intensive, you don’t have to fork out big bucks for an impressive display pieces.
As far as lighting goes:
I had an evening heavy hodos at an antebellum mansion that is a state run historical sight. No food allowed in the house, just on the veranda and with limited electric supply. If candles were lit the fire department was required to be present (and financially compensated), and absolutely no torches, not even in the garden. The site director was happy with floating candles, if knocked over the water would extinguish the flame. I used several glass pedestal bowls and the reflective property of the water was great. It’s a mood thing.
Jumping off into mixing water with light: I’ve seen some lights that float in water on several floral web-sites. I’m not sure if they are “glow sticks” or what, but they come in a variety of colors.
I know that all of these suggestions are heavy on the “decoration” side, but I have always found good inspiration by seeing the florists get creative.