As someone who tends to prefer cardio routines, I've never been completely comfortable with strength training. My great fear is that I could be inhibiting my own hopes to run a marathon by adding muscles. There's also the fact that I just don't like it as much as running or other exercises.
After spending what seemed like an eternity looking online for the right type of routine, I finally splurged and bought The Men's Health Gym Bible. Not only does it layout a bunch of gym exercises, but it also provides some guidance on the proper routines depending on whether you want to eventually look like Schwarzenegger, or if you just want to burn some fat and tone up. So I went for the fat burning, total body routine.
It basically works like this: alternating routines (A-B, A-B), done every other time I go to the gym. For example, today was my A routine. It's a series of eight exercises, all focusing on one part of the body. You have the option of one or two sets, and I usually do two sets of each. The idea is to move through the routine quickly and rest for only thirty seconds per set.
My A routine consists of dumbbell squats (lower body), one-arm rows (lower back, biceps), dumbbell lunges (lower body), dumbbell bench press (chest, triceps, shoulders), reverse crunches (lower abs), lat pulldown (upper back), russian twists with dumbbell or other weight (upper abs), and finishing off with a leg press. The book recommends going with free weights instead of machines as you work more muscle groups that way, and I have noticed that free weight exercises do seem to provide a much more complete workout.
So when next I go the gym I'll do my B routine, which is another set of eight again concentrating on the various muscle groups.
I've seen many different types of routines and tried several, and so far this has been my favorite. This lets me get in some strength training without overtaxing my muscles. What's more, the added muscle will help burn more fat, so it's all good.