alternative tagging databases for iTunes

I just started using iTunes as my music database. For that reason I started to rip all my CDs. Much to my surprise iTunes doesn't find the metadata (for tagging) for a lot of my CDs. I know the data is on discogs.com and sometimes even on amazon.com. Is there a way to automatically retrieve the data from those alternative sources. Just like media monkey does? It is really annoying to manually tag all those CDs.