One site that was recommended to me is Trello. It's a very flexible project management/to-do/brainstorming tool. It's organized as a number of boards, each of which has one or more lists or cards. You can move these cards between lists and between boards.
The general workflow I've established is to create a board for each project I'm working on, and have three lists: to-do, doing, and done. As you might suspect, cards start out in the "to-do" list, move to the "doing" list when I start on them and go to the "done" list when I finish. However, the tool, as such, does not force you into any particular workflow. That's an important consideration for me, because I've abandoned other task management software when its theoretical workflow model failed to match my real world needs. Trello is flexible enough to allow me to easily construct my own "pipeline" for tasks, with as many or as few steps as necessary, and have different pipelines for different projects.
Trello is a hosted application. However, they have a fairly easy-to-use export function that exports your boards and cards to a JSON document, so you're free to walk away with your data at any time. They also have an API, which you can use to further automate your task management.
It suddenly occurred to me that not everyone uses a website I love. Of all the websites I browse if you asked me which one improves my standard of living in the largest, most concrete way, it would be slickdeals.
What it is: a community driven "hot deals" website with voting. By itself this is already useful, but the best feature is deal alerts. you never have to actually browse slickdeals. Just create an account, set up deal alerts for whatever strings interest you (I for example have a deal alert for "whey" to get alerted to deals on whey protein powder).
More than 50% of my belongings come from sales I've been alerted to via slickdeals. Any big ticket items I need, but don't need immediately I just set alerts and wait. My laptop, desktop, tablet, smartphone, clothes, toiletries, books, games, even some food are all slightly better for the price I paid than they otherwise would have been.
So what other sites am I missing out on that would make my life a lot better?
A website I just discovered for habit building chains.cc seems cool, but I haven't had time to evaluate its usefulness yet.