Situated an hour south of Arugam bay lies the cove of Okanda. The wave offers sweeping rights that stretch from the rocky point right up to a closeout on the beach. The best time to visit is between May-September, when the monsoon season is impacting the western coast. . I travelled through here in July and the swell even produced 6 ft barrels! Make sure you arrange a tuk tuk the night before so you can arrive at the beach early. Allow provisions for a full day with plenty of food, water and sunscreen. Zinc is scarce and expensive in Sri Lanka so bring a few sticks from home - you'll need it.
I stayed at the 'Long hostel' in Arugam bay, owned by a quirky German/Sri lankan couple. The staff are friendly and the accomodation is a stones throw from the main beach. Chill out in one of the hammocks on the lay days or grab a beer from reception and hang with the many travellers that frequent the hostel. I booked through Hostelworld and found the reservation to be a breeze!