Is there a website where you can type in words to see how often they have been used in web searching?

I remember a while back there used to be a pay per click website that would let you type in key words or phrases for free to see how popular they were for web site searches. You could type in a group of words multiple ways to see which was used more. It was useful in coming up with meta tags for my web site. Is there anything out there like that now?