Visit website Support Details and it'll quickly round up your system information, including operating system, browser, IP address and more. Sure, you know that info by heart, but the site comes in particularly handy when you're helping someone else out.
Next time you're helping out uncle Hank and aunt Marge troubleshoot their computer and all they can tell you about their system is that the lights are on, tell them to type supportdetails.com into their browser, enter your email address in the form and send the details your way. (You can even pre-fill the form with some URL tweaks if you want to make it really easy.) It's not the most in-depth system information you'll ever see, but it's probably the simplest to get to when you're helping someone who's not all that computer literate.