First, I'd like to thank the poster who suggested onthegomap.com. I hadn't heart of it, but I immediately went to a hill run that I've used many times, which happens to be a portion of Garfield Avenue in Oxford, Mississippi where I live. It's .08 miles long and has an average incline of 12.8%. It's a bit flatter at the bottom--4% or so--and at its steepest it's 16-18%.
My usual workout up this hill is to run 4 to 6 x 60 seconds or so. I don't sprint it, just work it pretty hard, lifting my knees a bit. First couple of repeats a little easier; the others harder. I've gotten huge bang for the buck from this workout. I run about 5 miles before approaching the hill--3 to 3.5 easy, up and down rolling hills; the last mile to mile and a half at something more like tempo. Then take a brief break and hit it. Then, when the workout is over, fartlek another mile and a half back to where I've parked my car, which happens to be at the top of a very long hill, a steady 5% grade, although I hit that hill real easy.
What I've found is that this 4 to 6 x 60 sec. steep hill, repeated twice a week for a couple of weeks, immediately results in my easy pace and all other paces speeding up by 30 secs/mile. I don't have to hammer the repeats, just work them in a skillful way. By the time I hit the top, I'm going to be hurting, but the point isn't to build and hold an anaerobic load; it's purely to develop leg strength. And it works.