What is your favorite site?

I am always on the look out for great websites or free software. It can be anything from a photo editing site to money management software.

A place to find free music or connect with friends. A site that helps me to find the best deals on my travel plans or helps me plan an event.

What is your favorite site? I am inviting all of you to leave a comment here and share your favorite fun or helpful site or program on the web.

Thanks in advance for sharing your great ideas!