I have tried lots of tools but the most motivational one is my Thunderbird inbox: I don't archive / delete / mark as read an email until the task / request in it is done. Therefore I always ask to email me instead of PMing, Tweeting, skyping, etc. I want to see my inbox emptied so much that I force myself to complete tasks even if I am too tired.
Since I became a new mom shortly after getting into the Internet business, I say, this method is mom-approved
Everything will be ok in the end
If it's not ok, it's not the end