two-a-days are pretty standard for some styles of training, particularly in eastern Europe (Bulgaria in particular). Mornings are heavy load, evenings are high volume, with at least 6hrs between them. Charles Poliquin recommends a similar set-up, focusing on one or two body parts per day.
Another option, advocated by Chad Waterbury, is lower volume total-body routines twice-a-day. Again, high load in the morning, higher reps at night.
Finally, I've seen C.S. Sloan (I think it was him, but don't quote me) advocate one body part in the morning with a variety of loads and rep schemes, and an entirely different body part at night.
I've tried both Poliquin's and Waterbury's recommended routines of this style, and actually had far better results, strengthwise, with Waterbury's. My squat and deadlift hit alltime highs while doing that routine.