Excellent choice. The Mendelssohn Octet is the first piece of chamber music that I ever really got excited about, probably because it is so orchestral in its form and sound. I "borrowed" a recording from the college radio station (I'm sure they never missed it) and listened to it for days on end. Now I'm a huge fan of chamber music.
As for the cello, the solo repertoire is not extensive. That's probably because there weren't a whole lot of cello virtuosi running around Europe in the eighteenth and nineteenth centuries. There are, of course, the Beethoven cello sonatas (here's Rostropovich playing one
). Beethoven wrote a triple concerto for violin, viola, and cello, which is really just a string trio with orchestral accompaniment. Brahms wrote a double concerto for violin and cello, but frankly that's not one of his better efforts.
Seems like a lot of composers wrote a work or two for the cello
, maybe just to show that they could, but there was no equivalent of a Paganini (or even a Bottesini
) for the cello. Luigi Boccherini may have come the closest. He was a virtuoso cellist, and wrote about three dozen cello sonatas and a dozen or so cello concerti. He also often gave a prominent place to the cello in his chamber works, e.g. his quintet for two violins, viola, and two cellos, Op. 28, No. 2, G. 308. If you like Haydn or Mozart, you'll like Boccherini.