I stayed on South Beach after my cruise last year, at the Park Central Hotel, which was expensive, but I had always wanted to stay actually in an Art Deco hotel.

I did a lot of research beforehand on http://www.cruisecritic.com If you go to the Florida Departures board there was a lot of help re south beach accommodation on there.

As part of a cruise the travel company booked us into the Dorchester Hotel on Collins Avenue. Reviews were not brilliant and are still mixed 2 years later, but we found it ok for 3 nights. Location is its saving grace, just across the road from the beach and 5 minutes walk to the Lincoln Road Mall which is the main area. We never had breakfast in the hotel because we were so close to the Mall and lots of the shops there have ticket offices for any day trips you want.