Strength and conditioning for Endurance running by Richard Blagrove is a good book. I have listened to a couple of podcasts he's been on. He is now Dr Blagrove (PHD in exercise physiology or something like that). He recommends strength training 2 x per week for distance runners. 1 squat exercise, 1 lunge exercise, 1 step up exercise and 1 hinge exercise per session for lower body and a push and pull exercise for upper body conditioning. I think he was keeping things simple for the podcast and that is if you were time limited. He is big on neuromuscular adaptations and lifting fairly heavy rather than just body weight etc. He works at Loughborough uni and has worked with some top athletes there. His book has some useful examples sessions and also how you can fit them into a training week.