Millions of people take the London Underground to and from work every day, and it's a miserable experience for nearly all of them. It's crowded, hot, and there's nothing worse than arriving on the platform to find that your desired service is cancelled or running sporadically. You can arrange for Transport for London (TfL) to send you service updates via text message, but for the truly organised, TubeBuddy is a superb - free - application to have.
You can find out how each London Underground line is performing, in more or less real time, before you've even put your shoes on in the morning. Then, you can set the application to check the Tube again at a particular time in the evening.
Even more cleverly, it connects to the TfL network to give you live departure information, telling you how many minutes until the next train to your destination leaves, and even exactly where your train is. This is of limited use if you use the Tube at peak times, when trains run every minute or so, but if you're trying to get home later in the evening, early in the morning, or on a branch that runs less frequently, knowing how long you're going to have to wait is a godsend.
If you use the Tube every day, TubeBuddy is essential. It works superbly and the ability to get it to automatically check conditions means you'll have the latest info even if you forget to look it up before you leave your desk. Even if you don't use the Tube, you can always check conditions and remind yourself your own commute could be worse.