Stretching
Opinions vary widely on the benefits of stretching and when to perform stretching (before or after running). Essential Stretches for Runners is a great resource.
I have found it useful to perform some stretching before runs as a sort of warmup routine. I believe stretching after runs is even more important, to avoid or reduce tightness following your run workout.
Foam Rolling
Foam rolling has proven to be another valuable method to undertake before or after running, or especially on days off from running. This Runner’s World article provides some foam roller exercises to help runners prevent injury and improve performance.
Massage
Getting a full body massage within your ongoing running training can be very helpful in keeping muscles loose and relaxed, and in flushing lactic acid and waste out of your muscles. Massage focused on legs seems especially helpful to runners, but it is important to not get a massage too close to an actual race date. It is preferable to have a massage a few days before a race (to allow waste to move out of your body before the race) or a couple days after a race (to wait for swelling to subside). Check out this article about massage for runners.
Ice and Heat
Other items to consider in treating your muscles and feeling relaxed and in reducing swelling:
Ice baths – especially soaking body in ice water from waist down. Ice baths are very effective in reducing swelling and inflammation experienced after long runs. I like to freeze water bottles and put them in a bathtub as a reusable ice bath solution, without continuously buying bags of ice. I usually soak in an ice bath for 10-15 minutes after a long, hard run.
Sauna or hot tub– sitting in a sauna or a hot tub can be relaxing for some runners, and it helps persons “sweat out” waste in their systems. An added side benefit can be acclimating your body to operating in very hot temperatures, as a preparation for warm weather races. A caution is to not sit in a sauna for an excessive amount of time (recommendation: no longer than 20 minutes at beginning), and don’t have a sauna session immediately after a workout to prevent overheating.