Here's the one I did. It was paper pieced, but it could probably be done as applique also.

http://www.quiltingboard.com/t-34242-1.htm

http://www.quiltseeds.com/catalogue.html
If you scroll down to the Tides pattern or the one with the beach chair, they might be fun?

I made one a few years ago with free colouring book pages done in machine appliqué, but guess I don't have the picture in this computer, but you could check out that option for ideas.

Very nice. I like this one.

You could adapt this to a beach quilt.
http://www.hoffmanfabrics.com/EDocs/...%20pattern.pdf

If you decided not to do a themed quilt for the beach house, you could make a traditional quilt with blocks made in "beachie" colors like shades of blues or sandy beiges.

I have some really neat wallpaper border in my bathroom that my son adapted to painting on the window that's right over the shower/tub. It would make a really pretty wall hanging...waves coming into the beach, white lawn chairs grouped with an umbrella, a few shells scattered about, some seagulls in the sky along with puffy clouds. Could add a sailboat or lighthouse off to one side.

Here's my lighthouse quilt that I PP years ago and finally finished it...The beginning of this year I think.

Window quilt with fish, dolphin sandy border. Would be fun.

You could make a very simple scene of a sunset over water. Maybe take some photographs or have your sons take some and adapt them to a simple landscape quilt.

Thanks everyone for the great advice. I will post pictures later.