There are a lot of ramps in Pinellas County, throughout the Clearwater/St. Pete area. Courtney Campbell has a good beach on the west side of the causeway (Clearwater side), but unless you have a big gas tank, there isn't much to see.
Dunedin Causeway is the best. You have easy access to the intercoastal, Gulf, and the area is beautiful to explore. You can zip down to Shephards and many other waterside restaurants and hang out, see the big houses (including Hulk Hogan's) on the intercoastal, and catch some swells in Hurricane Pass.
I personally haven't been to it, but Fort DeSoto park is also supposed to be awesome. That's down in St. Pete. The ramp there is supposed to be huge. I know the waters around that area are incredible- that's a good spot to ride.
There is also a small launch I go to near John's Pass (it's actually on Boca Ciega Bay) that is usually pretty empty...I think it's off Park and Starkey somewhere- been a while.
http://www.boatclix.com/links/boatramps.html
http://bigpinellas.com/fish/boatramps.shtml
