We supply the X Brand Hooks, these are one of the best around. They are very strong and made from quality metal that will not bend.
They are available in four sizes. For more information Click on the size you think you need for the weight specifications.

Hanging tip!  If you dont want your picture to start tilting on the wall over time, EITHER hang on two hooks (at either end of the frame hooked under the cord) OR stick a couple of bits of blutack on the two bottom corners of the frame.