Check out Mezzanine on the cliffs only 40 feet high but nice overlooking Playa Paraiso. Superb Thai food and great ambiance and a super view. They even make decent drinks too and have good shows on Friday and Saturday nights.
For the budget minded, try Pollo Bronco in Tulum 'Pueblo'. Pollo Bronco and Pollo Asada both offer chicken that is roasted to perfection that can be ordered by the 1/4, 1/2, and whole.
It should be noted that most of the restaurants in town are infinitely cheaper than those at the resorts. Most places, with the exception of the italian and japanese restaurants feature entrees for well under 100 pesos, or 10USD. Don Cafetos features authentic mexican and is one of the most popular restaurants on the strip. There are countless little cafes and establishments to get a great bite to eat for cheap.
If you want non perishable items, grab some snacks to supplement your meals at the Super San Francisco Food Mart. You can buy a cooler here which is great for having cold drinks on the beach each day. Just pick up ice in the morning and the cooler will stay cold until night time. This supermarket however is run by locals and hardly anyone speaks english, so if you don't know spanish, be prepared to shop around to find what you need.
If you are staying on the beach, it is wise to stock up on food and drinks in the pueblo.
There are not too many restaurant options on the beach, and the ones that are operational are quite expensive.