I know that there are alot of stuff out there for making water, but what would you all recommend for using to make a beach scene?

Also, how do you do the borders; meaning the water will touch three sides of the dio, so how do you keep the stuff from running off the dio?

Well, as for the edges, you make a little frame or edge for the base, like a picture frame, or just simple strips like this:
http://www.inpayne.com/models/seaview_pl1a.html
http://www.inpayne.com/models/pegasusmars1.html

I wouldn't know what to use for water material for a beach scene, though. For that seaview of mine, I just used modeling paste and a butter knife to make the sea texture.

Woodland Scenics has a lot of water making materials. They have some that are thicker that you could use to build up waves, foam, etc.

You could try 2-part epoxy resin glue with the right paint colours added; good points are that it dries looking 'wet' and is see-through, and doesn't need to be painted on its surface as the colour is already inside the 'water'.
Bad points are that as it dries it flattens to leave a smooth surface, so you have to keep roughing up the surface right up to the last minute; and that for a large diorama you'd need several packs of the glue.
Here in the UK the discount shops sell cheap 2-part glues at four tubes for £1, so it can be obtained fairly cheaply, and for a diorama water effect it doesn't matter how good it would have been as glue!

Thanks all for the ideas.

Don't forget to post pix! :) rr