Logging a lot of miles on the road can make Jack a dull boy and the legs thick with lactic acid...

I find that incorporating a variety of other things makes a big difference in recovery, and in keeping the legs fresh.  Periodic sports massage with myofacial release  is a must do.  I have a buddy who does IronMans in the SouthWest, and he swears by weekly massage and or acupuncture (I've not done that yet).   I find swimming is a great XT workout that has zero impact on my running muscles (as I don't kick much), can do almost anytime, and is relaxing and puts me into a completely different atmosphere.  Biking is also great for XT, but hard to do here in the winter (altho I got out last Sunday and got in an hour and a half as temps were in the 40's for the first time in a long time) - biking with the trainer is kinda boring - some of the bike clubs have 'group rides' where people bring their trainer and ride to made-up "races" with clips from the T.-de-F., etc.  In Minny, I love to go snowshoeing or X-country skiing - fewer places to do that here.  I also like to do some boxing as an alternative - have a big bag and a speed bag in the basement in MN.

When doing a lot of running, I don't really care for tennis as it's just too different and I don't want the blisters.   Buckets, rowing are always good XT activities as well.   Lastly, Bikram yoga (only kind I have tried) is a good XT activity - I am sure there are many other varietals that would be good as well.