I sent a link from my last Sustainable Running Post to my trainer Christine and she came up with some more...very thought provoking...
1. Core work - adding in extra strength work (with a personal trainer!) or pilates/yoga
2. Reassess your form - are you hunched over? Are your arms swinging with elbows wide? Your form and gait is critical to injury prevention and sometimes it is necessary to ease off on pace to get running technique fixed and then start to build on speed again.
3. Weights to build leg strength -weighted squats/lunges assist in building stamina and strength without you having to do the repetitive work pounding the pavements
4. De training ie after a long race and training period taking a break, mentally and physically, cross training (swimming which you mentioned, or cycling to keep aerobic fitness and muscular strength but lose the impact) and then building back up safely again - your body will benefit and you will be able to compete year after year as opposed to constantly pushing the boundaries and getting worn out physically and mentally.
5. LISTEN to your body - if you are worn out and not enjoying running and losing motivation then rest and reassess, running should be for enjoyment and fitness not be a chore so reassess and make changes if you are becoming stressed or lacking balance in your life - and then it will become a pleasure again!