Classical Scores Library by Alexander Street Press is a great resource to discover compositions for your instrument and ensemble. New and old compositions can be accessed and printed.
Different titles and languages can be used to describe any one piece of music. For example, the same piano concerto by Mozart can appear as:
To allow for these variations in titles, music scores are catalogued using 'Uniform Titles'. Uniform Titles are collective titles that group similar forms of a composer's music together. For example, all of Mozart's symphonies are grouped by symphonies, concertos are grouped by concertos. This is why it's important to search the plural form (concertos, sonatas, etudes, suites) in your keyword search. The Uniform Title for the above example would appear in the catalogue as:
A common practice for opera arias, art songs and other lyrical works is for these types of works to be listed in Library catalogues and other information sources in their original language. For example Schubert's famous song "Gretchen at the spinning wheel" will be appear in the Library catalogue in its original language as: Gretchen am Spinnrade. Consult Grove Music Online to find the exact title.