The best starting point for any research is the Libraries' InfoKat Discovery and your course reserve list. Be sure to check bibliographies & indexes!
Although encyclopedias may not be cited in research papers, they often have bibliographies with good sources that are appropriate to cite. Grove Art Online and several other dictionaries and encyclopedias are provided through Oxford Art Online. The best database for locating monographs, exhibition catalogs, anthologies, etc., is the Bibliography of the History of Art & International Bibliography of Art. WorldCat is also a good database to search by subject or keyword. When you are trying to verify titles or other bibliographic information, WorldCat is the ultimate source. It links directly to InterLibrary Loan, so you can request the materials you find in this database if they are not here at UK.