There are scores of these sites out there, like http://oplop.appspot.com/. The nice thing about having a small application do it is that you don't have to run it on a browser, which I inherently trust less... all the same, it's pretty convenient to have it on a web page (e.g., when you're trying to enter something in on your mobile phone, or on a device that isn't yours).

My favorite password manager, pass, is fantastic, but unfortunately I can't use it if I ever leave my laptop.