http://en.wikipedia.org/wiki/Equine_conformation
I was looking for the standard drawing of a conformation horse and came upon this. I skimmed through it quickly and liked what I saw. Maybe this can help or show people what to aim for if they just MUST breed their horses. Pick your breed of choice, learn what to breed for (if you just must) and give your horse a chance in life. ETA: Whoops, almost forgot to add...the above site also can show you a lot about what to look for when you're in the market to buy too. That plus plain ol' experience will really help you. As time goes on, I'll have plenty to say about buying a horse too.
A disclaimer though...I have ridden horses that looked like a committee put them together and they never went lame and rode well. This can happen but by and large, a well conformed horse will hold up and do what you want without the undue stresses (example: Dressage) and probably last longer than a badly conformed horse. More on this later though.