Academic Search Complete - a multidisciplinary database of more than 8,500 fulltext periodicals with pdf content going back as far as 1887.
Literature Criticism Online is a part of the Literary Reference Center Plus -- Includes full-text articles from scholarly journals and literary magazines. Also provides critical essays, work and topic overviews, full-text works, biographies, and more to provide a wealth of information on authors, their works, and literary movements.
Project Muse - provides reviews from scholarly journals
JSTOR - a shared digital library that includes the fulltext of more than 2,000 academic journals, dating back to the first volume published. Coverage varies depending on the journal title.
Lexis-Nexis Academic -- full-text newspaper articles including reviews and criticism
ProQuest Newstand -- news sources from around the world
New York Times -- The Music Section
Alex Ross -- Music critic for The New Yorker
A useful E-book on writing professional reviews,as well as music in general.