For the last 8 months I have been doing a workout from MTB Strength Training Systems called DB combos. At first I pretty much followed the workout to a T as it took me a while to get the movements down and learn the new exercises that I had never heard of before. Once I learned the exercises and got the movements down, I was able to start adding things to the workouts and creating my own based on what I felt like I needed more of and what I enjoyed doing most.
There are a LOT of benefits from adding a program like this into your routine. Some of the benefits I have discovered are, less overall fatigue on the trail, more explosive power, more core strength and less back pain, less arm pump, better posture on the bike and more fluid movement patterns, and just a feeling of better general fitness overall.
One of the really unique parts of the particular program I have been using is the high tension cardio combination circuits. Basically these are weighted aerobic type workouts that focus on movement patterns that you use on the bike. They are like doing sprinting intervals on the bike with short recovery periods in between to speed up your recovery time, except you use weights and you aren't on a bike. Check out this link for more info on the benefits of this type of workout.
While they seem like a lot of work, I have found learning these exercises to be a pretty fun experience and something fun to do in addition to training rides on the bike. This is definitely not a substitute for riding, but like I said, will help you get more out of the time you do spend riding. At least it has for me.
Some of the exercises that have helped me the most are deadlifts and variations of that exercise, single leg squats and variations, and kettlebell swings. I would go into more detail but I am not a strength coach, nor should I pretend to be. If you decide to use a program like this to get stronger on and off the bike I recommend you either hire a coach locally who uses similar methods or purchase a program like this that explains each exercise in detail. Movement is the key to getting the most out of this program, not the amount of reps or weight you lift.
I have no affiliation with MTB Strength Training Systems, I am just a happy customer.
Here is another program available in B.C. that 3 of the fastest enduro racers in the world have been using. It looks very similar to MTB Strength Training Systems. http://marxconditioning.ca/
Here is the program I have been doing. Only $37!!! Even a broke ass unemployed electrician can afford that!