This is my #1 secret:
Yep, its a $7 kitchen timer.
I set it for 50 minutes. I do nothing but work for those 50 minutes. I dont check email, I dont answer the phone, I dont answer the door, I dont play videogames, I dont read instant messages (unless its directly related to the work I'm doing, such as with my coders etc), and I dont read forums during that time. Dont try to interrupt me during that time, because i simply wont acknowledge anyone. Thats MY time.
Then i take a 10 minute break, grab something to drink, go the bathroom whatever. Then i do another 50 minute cycle.
After that 50 minutes, I take a 40 minute break. Have a snack, check email, do something in the garage, whatever. This total of 2hrs 30mins is one work unit. Keeps me refreshed and productive, and not bored & burned out. Doing 3 - 5 of these a day, gets alot of shit done.