Two hours and a world away from the popular tourist digs at Kuta and Legian lays the sleepy Medewi Beach. It's a mishmash of boulders, pebbles and black sand and is well regarded for surfing of all standards, with one of the longest left-handers on Bali — 150m on an average day, an amazing 400m on a good one! This is a sand and boulder break though, so the waves don't get too big and there is no reef to slice your feet up on though. There's also a smaller right hander nearby.
The beach hasn't been given over totally to surfing though and there are plenty of fishing boats pulled up on the shore. There isn't too much to do here other than surf though, so if you're in a surfing party but don't surf, pack some books. Swimming is better here than at Balian, but still carefully keep an eye on the currents.
This is an especially lush part of Bali particularly between Medewi and Balian. If you have your own wheels (preferably a motorbike) there are plenty of areas well worth exploring both on the beach side and off beach side of the main Gilimanuk to Kuta Road. Anywhere along the coast of this part of Bali can expect brilliant sunsets.
The selection of accommodation in Medewi isn't the greatest in Bali — especially at the budget end. So plan to stick with fairly rudimentary offerings of to spend a little more than you are used to.