I've been working a lot in the past few days to get good beach terrains. Either they work good for empty beach lots, which I hate building, or they only place a very few of the premade lots out there.
Sophisim did an excellent edit of the Bon Voyage neighbourhood Twikkii Island (http://modthesims2.com/download.php?t=251942) but I play a rather large neighbourhood with all of the Maxis pre-made Sims, so I need a lot of space to plunk down all their houses!
(http://bluesoupistan.com/bluesoup/files/Misc/TwikkiiExpanded_bigger.jpg)
I edited Twikkii Island once more, and added an upper flat area for more houses and of course a road from the lower section so your Sims can visit each other! Now I can play all the great lots by keef1973, (http://modthesims2.com/member.php?u=223325) which were made with Sophisim's edit and of course don't seem to fit properly on any other custom neighbourhood, since beach lots are so finicky about placement. This one is awesome for playing many beach lots, and they don't all need to be ones you create either, for those who hate building as much as I do!
Bon Voyage is not needed, though of course it's recommended to get the most out of this neighbourhood with all of the beach lots.
You will need some sort of camera fix to see the whole neighbourhood properly; I recommend Gunmod's camera mod (http://www.modthesims2.com/showthread.php?t=97642) on this site.
Download here (http://bluesoupistan.com/bluesoup/files/Misc/TwikkiiExpanded.zip)
To install, unzip and place all files in My Documents/EA Games/The Sims 2/SC4Terrains.