Piano sonatas (Beethoven)
Ludwig van Beethoven wrote his 32 piano sonatas between 1795 and 1822. Although originally not intended to be a meaningful whole, as a set they compose one of the most important collections of works in the history of music. Hans von Bülow called them "The New Testament" of the piano literature (Johann Sebastian Bach's "The Well-Tempered Clavier" being "The Old Testament").
Cello Sonatas Nos. 1 and 2 (Beethoven)
In the early 19th century, sonatas for piano and instrument were usually advertised as piano sonatas with instrumental accompaniment. Beethoven's first violin sonatas, for instance, were published as "sonatas for piano with accompaniment by the violin." The cello sonata was especially so plagued, as it grew out of sonatas for continuo; as late as the beginning of the 19th century it was still common for the cello in cello sonatas to double the left hand of the piano part, with the piano right hand playing "obbligato" figurations and melodies. Beethoven, indeed, is credited with composing one of the first cello sonatas with a written-out piano part.