I totally relate to the topic, I ran into same motivation problems over the last two years, having your own company is a thrill, but the contract-less periods were killing me, slowly making you addicted into web-browsing, retro tv streaming, indie games and other work-consuming related topics... and that is very hard to get out from once clients are knocking on the door.
I looked around for motivation tools, and found the pomodoro technique. Principle is a to do list per day, with a side list where you write down all tasks that carry out from one day to another. Then you break down each task in kitchen timer units (25 minutes each) and estimate how long each task will take. Each unit cannot be divided, if you get interrupted by yourself (a sudden need to browse a game development forum, for example) or someone else (phone call) you indicate that got carried away from the task at hands and void the unit running to start it again.
Basically, at the end of the day, you have a to-do list filled with units completed and interruptions, indicating how many 'real' 25 minutes you dedicated fully to the task, and how many times you got interrupted by yourself or others doing so.
Bad points: you need to be honest with yourself, and that's not easy at start.
Good points: you actually have after some days an accurate timesheet of all your activities (in my case, I use this for billing and evaluating). You actually get some work done during these 25 minutes and don't feel guilty not working when taking a break. Having a real kitchen timer and paper worksheet actually felt more tangible than any software app tracking time, it worked better for me, and actually slowly indicated people around not to interrupt before the ring!
(I'm not selling anything here, all downloadable content is free. You can order your kitchen timer from them if you feel like giving back, though)