In addition to using water-resistant SPF products and applying them often, consider providing protective sun wear for everyone in the family, specifically shirts and hats.
For kids and babies, the UVSkinz brand has a broad variety of sunwear. All have a UPF 50+ (the UPF refers to fabric instead of the SPF in lotions, sprays, etc.). The site also provides a lot of information about sun protection.
prices vary, $15.95 and up at UVskinz.com
UVSkinz also has a really chic wrap top for women. It's actually possible to be protected and fashionable at the same time! $36.95 at UVskinz.com
For active adults, Golite has really a nice runner's shirt that is perfect for the beach. Their Wildwood Trail Shortsleeve Run Top features lightweight fabric with an extra fast dry time and an UPF of 50+. It is specifically designed to protect the skin from the sun without the risk of overheating. If you snorkel - be sure to wear a shirt!
The Coolibar Packable Wide Brim Sun Hat ($30) is made of lightweight, breathable fully-lined polyester knit and has an UPF 50+. The broad 4" brim shades your face and neck and it has an internal sweatband and drawstring for comfort and great fit. This hat can also be hand washed and will retain it's shape after it's been folded! CharlestonNaturally.com has lots of options for men and kids too.
Many designer glasses do not provide broad spectrum sun protection so make sure you read the tags before buying a new pair of sunglasses. Ryder's Eyewear has a number of different styles, my favorite for women is the Dutchess from their Chill-Essential collection ($39.99).
The lenses are shatterproof, optically-correct, scratch-resistant and provide 100% UVA, UVB and UVC protection. Ryder's also has several cool sunglass styles for men.
View the entire Ryder's Chill-Essential Collection for men & women.