Researching Original Titles Of Works

I am especially interested in being able to uncover the names by which the works of, e.g., Mozart and Beethoven were originally published.  Scans of first editions presented at the Harvard Collection's website have whetted my appetite but leave the picture incomplete. 

I understand that for certain composers this information is easier to come by than others, e.g., there is an entire website devoted to scans of Chopin's first editions.

To make this request the most simple, is there a source, if only a list (although I am quite curious to see actual cover pages), of works published during Mozart's lifetime and their respective titles?  Eventually this will apply to other composers but I realize how broad a request that would be.