Luckily you can go east or west and find a beach within 1-1.5 hours. It all depends on what you're looking for.
Blue waters, and some beaches with lots of shells to be found on the Gulf side. In '07 we went to the Tampa area and there are gorgeous beaches around there, with some of the best in the world. You can find tons of shells around there too.
We went to Cocoa Beach in '06 and would have liked it a lot more had it not been for the chilly weather (February, and had a cold front move in the day before!).
In Nov. 08 we had our 3rd WDW trip and went to Daytona Beach this time. We LOVED that beach. It was a beautiful day, the waves were fairly calm, and you can drive ON the beach. It's a really different type of sand (kind of reminds me of Moon Sand). There's a really good restaurant right on the water called Ocean Deck, and there's a pier area w/ a sky ride, shops, etc. I wish we would have spent more time there. Hardly any shells at this beach though - but it was great in so many other ways.