Hills Are Your Friends
Hills are some of the best speed work there is. If you want to shatter your 5 or 10k pr but you are tired of speed work try some hills. If you are tired of running repeats over the same 800 yards try hills. Try running hill repeats or just add hills to your daily route.
Just start at the bottom and charge up at top speed 3 or 4 times depending on the hills. Parks with lots of hills are great. Just take a run through the park a couple times. Then take a nice cool down 5k on pavement for a great workout.