* Cramming/putting stuff off to the last minute helps with motivation. I did it too much and burned out. Find the right balance.
* Oftentimes I find that lectures are a really inefficient way to learn stuff. For example, in one class I can get through the slides of a 90-minute lecture in 45 minutes on my own, have more fun, and understand better. The key is actually getting myself to do this. Also, it's important to have a timer and glance at it frequently to make sure I'm keeping a 45-minute pace.
* Use triggers and condition yourself to concentrate on the triggers. For me it's original-flavor Trident gum + rainymood.com + somafm.com/play/groovesalad.
* I generally work in cycles: 50 minutes of work followed by a 10-minute break where I change my scenery and daydream. I rarely try to make myself work when I'm seriously not in the mood, as I don't get much done and I create a negative association. I don't hesitate to take much longer breaks if my morale or energy are really low.
* Every evening, I plan out the next day and have a rough idea of what I'm going to be doing at any given time. I generally don't follow my plan very well, but having a specific thing that I'm supposed to be doing seems to lower my activation energy for tuning out distraction. I use cron to open a tab in my browser reminding myself to make a plan, and I stick my tongue out until it's done.
* I'm pretty good at sleeping 8 hours a night. I think this helps me because it increases the portion of my days on which I feel energetic.
* Studying with other students always helps with motivation.
Why are you taking so many classes? At my university you need special permission to take more than 5 or so.
This site is probably good for more advice: http://calnewport.com/blog/