The best-kept secret among party planners is Avi Adler (87 Luquer Street, Brooklyn; 718-243-0804). Avi and his partner, David Stark, both former painters, create modern, fanciful designs in their Brooklyn studio -- like the wall of 8,000 lemons smothered in baby yellow chrysanthemums they mounted for an Esquire party. While their work can be edgy -- for the "Brite Nite" gala last month at the Whitney, they fashioned an aerial landscape from 5,000 Swarovski cut crystals meant to look like "stop-action rain" -- and their client list intimidating (Estée Lauder; Goldman, Sachs; Louis Vuitton; the New York City Opera), they assure us that they are not above putting together fabulous flowers for the ordinary Joe's event. They will not do single arrangements, however. For that, you'll want to call the up-and-coming Spruce (75 Greenwich Avenue; 414-0588) or Belle Fleur (11 East 22nd Street; 254-8703). Spruce has developed a dedicated following for its simple, whimsical arrangements, like its trademark wooden crate full of roses, tulips, and sweet peas. Belle Fleur's bouquets are more flamboyant; even its least-expensive arrangement ($50) -- an orange glass vase brimming with pink and pale-orange roses and fragrant hyacinths -- seems to explode with enthusiasm. Hotelier extraordinaire André Balazs, who sends flowers on almost a daily basis, is partial to David Brown of Flower Shop (399 Bleecker Street; 352-1224). "I use him for all of our personal things, and for everything we do at the Mercer hotel and kitchen," Balazs says. "He has an exquisite eye, and always seems to find the most exotic and erotic vegetation."