Many professions had their own directories and if your ancestor was a professional gentleman (women were rarely "professionals") in the 19th century he is possibly listed, perhaps with details of his career.

A typical example is Crockford's Clerical Directory which lists details of Church of England Clergymen and was first published in 1858. Others cover the Army Officers (Army List since 1754), Naval Officers (Navy Lists since 1749), Medical Doctors (the Medical Directory since 1845 and the Medical Register since 1858) and Lawyers (Law List since 1775). Lists of university graduates, in various formats, are also available.

Many other professional and trade directories exist, but usually of later dates.

The Society of Genealogists library has a very extensive collection on the open shelves, and many libraries have odd copies. Some will be available more widely on microfilm, possible through the LDS Family History Centres (for the catalogue and addresses see familysearch.)

If you can add to the information given above tell me.