The University of Miami has an archive of digital images and a timeline called “Travel, Tourism and Urban Growth in Greater Miami” available at http://scholar.library.miami.edu/miamidigital/ . True to south Florida, the front page is in pink and a tealish blue.
There’s an introduction to the overall project, but what I found fascinating was the timeline, which starts in 1819 which Spain ceded Florida to the United States. a variety of events are described on the timeline, and some have external pictures and other information added to them (maps, an article on the Seminole Indians, pictures of William Brickell, etc.) The timeline is divided into four sections and goes from 1819 to the 1990s.
The image gallery is viewable in several different ways. You can search by keyword, browse by topic type, browse by collection or location, or browse by resource type (including aerial views, maps, night photographs, or postcards.)
I did a keyword search for “beach” and got 38 pages of results — pages seem to have nine images each. Thumbnails are good-sized; all the results on the first page were postcards. The postcards looked like they ranged in date from around the turn of the century on up. Later in the search results I found letters, promotional materials, and newspaper images. Detail pages for each of the items provides subject, date (when available; many of the postcards I looked at did not have dates), repository, and collection. The images themselves are made available in a Flash viewer for easy zooming and panning.