David Popper
Popper composed a very large number of cello pieces, many of which are short pieces suitable for encores at a recital.  One of the most popular (and not too difficult) is the Gavotte in D major.  He composed a Requiem for three cellos and orchestra, and he wrote four cello concertos.  However, his most important work for cellists is a collection of studies called Hochschule des Violoncellspiels (High School of Cello Playing).  This book contains 40 etudes, or musical exercises to develop technique, and is widely used today by cello students to improve their playing.