Akumal Beach Resort is a few miles south of Playa del Carmen and I highly recommend it. It is a very reasonably priced all inclusive and the snorkeling is spectacular! Here are some photos from a recent trip with my daughter.
Akumal Beach
Akumal Beach Snorkeling
My fiancee' and I are planning an August honeymoon to Akumal, however we will be staying at a smaller non-all inclusive hotel just down the beach from the above resort. My wife-to-be is a certified NAUI scuba instructor and is giving me the instructional part of my training at home, and will certify me with the open water dives in Akumal Bay. I am SO excited, I can hardly wait to get down there and see the stuff which is to deep too reach with a snorkel.
If you want more info, feel free to PM me.