There's no shortage of to-do list apps and services out there. What NowDoThis excels at is eliminating the clutter and keeping you on track. Enter your to-do list at the start of the day, include a duration if you wish and hit Start. NowDoThis takes it from there.
You can use basic, natural language for your to-dos to enable a timer. So, if you want to start with a one hour cramming session, simply type "Study for 1 hour" and the service will create a countdown timer for you. You can give a duration for each to-do and, when the last one is done, the site will ding and you'll be prompted to start the new timer when you're ready.