Sinularia sp., Nephthea sp., Capnella sp., Cladiella sp. (Colt) can all get pretty large. Sarcophyton's and Lobophytum's can get pretty sizable, too.
Depending on the experiment, encrusting softies like Clavularia (virdis, et al), Briareum sp., and Anthelia (and other Xeniids) can cover large areas of rock in short amounts of time.