A number of scholarly associations have now created databases of artwork to replace traditional printed catalogues raisonnés.
Here are a few sources that have collected those sites:
And here is a great example of an online catalogue raisonné of an individual artist's work:
A catalogue raisonné, broadly speaking, is a reference work that provides as comprehensive and detailed a list as possible of an artist’s oeuvre. Sometimes the catalog of works is broken down by format or medium, or broken down into chronological sequences.
Oxford Art Online definition: catalogue raisonné
New York Public Library definition:
What is a Catalogue Raisonné?
Finding catalogues raisonnés in general:
The Fine Arts Library's collection of catalogues raisonnés is distributed; many of them held in the reference collection, while others are in the circulating collection (held either at Fine Arts or the Annex).
Finding catalogues raisonnés in the catalog:
The term, catalogues raisonnés, is usually used in the subject cataloging for art monographs. Here's an example of a search (using the advanced search function):
It is sometimes helpful to broaden the search to also include the terms, catalogs and catalogues (using the "any" query to search for either term)--be aware that this search will also look for exhibition catalogs.