Chrome: There are many time-tracking applications out there, but TimeYourWeb might be one of the simplest we've ever seen. It's a free Chrome extension with no login required, and it comes with some of the handiest charts around. TimeYourWeb has a few ways to see how much time you've spent on a site. While you're on a page, the extension icon in your toolbar will show you how long you've spent on a given tab so far, so you can see if you're wasting too much time at a glance. This alone is super handy for those times where you swear you're only going to check Facebook "for a minute".
For long-term analysis, you can view several different chart modes. Summary will show you a broad view of which sites you spend the most time on per day, week or month. Stacked view shows a stacked bar chart showing which sites took up the most of your time on each day.
The Flow mode -- shown above -- is where the real fun begins, though. This shows a detailed breakdown of which sites you were on minute-by-minute, separated by each hour. If you're a freelancer or just trying to gauge how much time you're really productive, this can identify your most productive hours at a glance.