Hi,
On your way down from Melbourne, try Jupiter Dive Center, in Jupiter. Great boat, good staff, easy going operation. They tend to do deeper dives (80+ range) so nitrox is a good bet with them.
In West Palm Beach, you could try Diving Solutions. They are in Riveria Beach actually and run the reefs and wrecks. Ask to dive the Governor's Walk wrecks right out side the channel. They are in 80' and if the current isn't running too hard, it's really a wonderful dive.
Starfish Enterprise out of Lantana is also excellent. Dove with them last weekend and had a total blast. Good operation, good crew and relaxed atmosphere.
Basically, everyone is at least good, if they weren't, they would be out of business real quick as word tends to get around.
Best of luck!
Lee