Coral Seas is a good store right in Margate. Owned by hobbyists, nice coral.
Barrier Reef in Boca also has some nice stuff sometimes.
Aquacon is also something you might check out. But they are known for not having the best treatment of animals. Cheap stuff, though.
Everglades are beautiful. So is Pennekamp. I'd hit the latter if I was choosing only one. Very beautiful.
Delray beach is my favorite of the beaches there- clean, scenic, in close proximity to the shops on Atlantic. Way fewer people than Fort Lauderdale strip (where Beachplace is). Beach Place has really gone down hill since the economic downturn, most shops are empty. If you do Ft. Lauderdale beach, do Las Olas. Also, you might check out Riverfront (las olas)- there's also a museum of science there (Discover/y?).
For sight-seeing you should also check out Vizcaya in Miami. Old mansion, must-see.
I don't know how long you'll be there, or who you're entertaining, but if it were me and I was there for a week-10 days my trip would be:
Pennekamp (2 nights, sun and scuba/snorkel, leave early then go to ... )
Everglades park (2 nights, rent Segways maybe, do paddling tour, leave early go to ...)
Vizcaya (stay all day, enjoy the area, then drive at night back to...
Fort lauderdale (maybe do Riverfront at night, Las Olas shopping and dining the next day, then the following day...)
Delray beach (park near Atlantic Ave, enjoy a beach day, lunch on the water, dinner at Dada's (my favorite restaurant, very relaxed, can eat outside, etc.)).
Feel a sense of accomplishment in your tan.
Cheers,
Angela