Powerful site for file conversions. Actually mind boogling number of types. But unlike my favourite Zamzar, this site does a lot more in terms of documents with their long list of supported conversions. You will not be able to find so many features on one site out there! So if you would like to covert your PDF to word or vice versa, or convert excel to csv format, then you should bookmark this site. Best of all, they have this ability to determine unknown file type and attempt to find a solution for you.  And did I mention all these are availble for free?