The best resource is Michael Watson's pmjs page: http://www.meijigakuin.ac.jp/~pmjs/trans/index.html
UNESCO: Index Translationum (for more than just English translations)
Japan Foundation: Japanese Literature in Translation Search
UMass Japanese Literature in Translation Page (2005 version)
(This version of the page has been removed by the library but it has more information on it than the newer link. The link is to a web.archive.org page; if that link does not open, try here—my captured version.)
By the way, UMass Library has other good Japan-related resources. Check it out.
UMass Has it Already Been Translated? (2010 version of same resource)