Cleaning MP3 Collection?

So a friend of mine once told me about a website and/or program that would sort through all of one’s mp3s, and help to fill in the missing blanks in the ID3 tags..

I went to look for it lately, and have no idea what it is. Does anyone have any good info about which programs are good at filling in missing data? Also he’d mentioned that the tool he used even helped identify things like mis-spelled artist names, and could consolidate them into a single artist, and so forth.

Program/website suggestions anyone?