WorldCat.org adds Advanced Search Page

From OCLC:

Advanced Search includes the general keyword search available from the WorldCat.org home page, but also provides the ability to search keywords in the title and author indices. You can combine any or all of these search fields for more precise results.

For an even greater level of specificity, you can limit your search results to items in a particular language, format and publication date range.

WorldCat’s Advanced Search also allows you to search by ISBN or OCLC Number for known items.”