SuperGenPass (http://supergenpass.com/) does that in a way that is more likely to generate strong passwords honored by sites (e.g., multiple cases, punctuation, etc.). It comes both as a bookmarklet, and, if you don't want to use that, a mobile version (http://supergenpass.com/mobile/) that you can store somewhere safe so it doesn't even hit the internet (e.g., I store it on my Dropbox account so I can use it on my phone). Works great.
There's also an extension for Chrome called SuperChromePass that allows you to generate your passwords outside of the DOM to prevent snooping, or use Ctrl-Shift-P to do in-DOM generation for convenience, depending on your preference and paranoia.
That said, I've been using SGP/SCP for all my passwords for about a year now, and I have only come across a single site that wouldn't work with the default, 10 character password scheme: ConsumerReports.com
All in all, I would definitely recommend this to everyone because it means you don't have to keep track of an encrypted password database or have any software installed on computers you use. If your computer crashes and you lose all your data, you just put SGP back on your bookmarks bar and carry on with life...
