simple strength training routine

Ok so I have cardio down pretty good. On days that I run a shorter distance I will some arm stuff with my dumbbells ranging from 3-8 lbs. and I will include situps/crunches and pushups. I will usually do 3 sets of 15-20 reps. I guess I am looking for some basics for strength training since I've never been with a trainer. I do have a range of dumbbells, a weight bench and an multiexercise weight machine in my basement. I have a whiteboard that I use, but would be nice to have set exercises that I do certain days- to just tick off. I feel like I'm floundering, so then I tend not to want to do it since I feel like it's probably wrong.