We spent several days just relaxing on the beaches. After the stress of getting married, it was just what we needed! Our villa was located in Apple Bay. A good beach for snorkeling and sunbathing. The swimming is fine once you get past the coral. We loved Long Bay beach as well... the restaurant there served a good lunch and the beach was really long and great for walking. There was decent snorkeling there too and good sunbathing too along with lots of shade for a nap under the palm trees. Our favorite on Tortola was Cane Garden Bay. Imagine a lagoon so clear, calm, and warm that it looks like a swimming pool. No snorkeling here but it's fine because the expanse of great restaurants makes you rather lounge in the provided chairs and try all of the cocktails.
On Virgin Gorda, the Baths National Park has the most beautiful lagoon and beach that I have ever seen. The water was perfect for swimming and there was a coral area nearby for great snorkeling. This place is so popular though, they bring day sails full of people to snorkel so go on the off days. All of the other beaches were so bare, we felt like the only ones on the beach, save for maybe 10 other people on the entire thing. It pays to go in the off season!