Khaki Campbells (250-340 eggs per year), Indian Runners (150-300), Welsh Harlequins (240-33), Magpies (220-290), Anconas (210-280), and Appleyards (200-270) are all great layers. Breed is important, and so is strain, so make sure you buy from a reputable breeder who maintains good laying strains, since that's important to you.
Beyond eggs, each breed has its own look, personality, and other qualities that make them better or worse for specific situations, and some are easier to find than others. Runners are funny looking (literally--they make me laugh--and I LOVE them) and skittish, and they are extremely amusing and also very hardy and great foragers--they're not too hard to find. Khaki campbells are the best layers but personally I find them boring both in looks and personality--plus they're even more skittish than Runners--but they're relatively easy to find. Welsh Harlequins (I have heard--never owned them myself) are calmer and peaceful, and have the cool advantage of being able to sex day-olds by bill color--I think they're unusual but not rare. Magpies are absolutely gorgeous and large enough to be a meat bird if desired, and they are stunning pond ornaments with their striking black and white pattern--very uncommon, bordering on rare bird. Anconas are colorful and large, and that is all I know about them (no personal experience) except that they are even rarer than magpies. Appleyards are very rare, very pretty, large and that is all I know about them (again, no personal experience) except that they are probably the most rare of the breeds listed here.
Good luck--whatever you get, you're going to love the eggs, and ducks are sweet and fun. 
(Edited to change my description of Appleyards, which I had gotten wrong initially...)