You going for NH types, distance, or sprinters, Kauto? NH is doing very well at the moment, with prize monies outstripping the Flat for all race types. Distance Flat horses are a speciality, whereas there are plenty of sprint and middle-distance (7f) races around. Although that does mean there are plenty of sprinters around to contest them. You need to determine what you're going to breed for (bearing in mind that NH buyers won't be seeing any fruition for at least four years and will be paying you accordingly), and then check out the list of the best sires in your group.
How much you want to spend on the sires is the next issue. From very limited but just as expensive an experience as anyone, you're probably best off using proven types to set up with. You can experiment with first-timers, whose fees will generally be cheaper as they establish themselves, but buyers are wary sometimes, and more wary still of breeders without a proven record or connection to another established breeder. If you have neither, I'd suggest sticking with proven sires in the middle-range bracket of fees, say around the £6-10,000 mark.
Check out the Top Sires lists and you'll see what they cost to send your mares to them, and what their progeny is selling for, and, in the case of established animals, what prize money they're winning (after all, you will get a breeder's prize in appropriate races in due course, and every little helps!). Good luck - you'll need it!