Strength Training. Here's what I do.
Being a personal trainer in London, people often ask me 'What kind of training do I do in my spare time?'
So, here is a typical strength session that I do. I don't go too crazy these days, with more focus on maintenance as opposed to goal setting. (I done enough of that in my running days.)
15 x minutes rowing to warm up, followed by dynamic stretching.
Squats. 4 x 15 reps.
Bent over rowing. 4 x 15 reps.
Bench Press (on swiss ball.) 4 x 15 reps.

Knee to chest. (abs) 5 x 20 reps.
Russian twists. 4 x 30 reps.
Cleans. 4 x 15 reps.
15-20 minutes of static stretching to cool down.
And sometimes I'll do this 2 or 3 times a week depending on my clients schedule.