Felix Mendelssohn-Bartholdy (1809-1847) composed many interesting and good chamber music.
There are eight string quartets, two string quintets, one string octet, two piano trios, four piano quartets, two cello sonatas, one violin sonata, one clarinet sonata and even more.

Some works I want to point out explicitly:

The first masterpieces of Mendelssohn are his piano quartet b minor op. 3 and his string octet E flat major op. 20. The second work often is called “Mendelssohns first stroke of genius” (he was sixteen) and indeed this work for doubled string quartet really is genius. But IMO the piano quartet he composed some month earlier is on the same level.
Both works are unbelievable mature and show that Mendelssohn was THE “Wunderkind” in composing, not Mozart (what Mozart composed at the age of 16 has not this quality). They contain a great richness of inspiring melodies, finesse and magnificent sound.
The two most interesting movements are the last of op. 3 with his dark atmosphere and Beethoven-like climax and the first of op. 20 with his friendly, almost orchestral celebration of joyous music.

Two years later Mendelssohn again raised his level – for the last time: IMO this level he topped never and only reached it sometimes again. I speak about the string quartet a minor op. 13. Mendelssohn (at the age of 18!!) seemed to be the only contemporary composer who understood the late string quartets of Beethoven and knew how to handle with this heritage.
This quartet is more or less concrete inspired by Beethoven’s a minor quartet op. 132 (at least the first and last movement) and like Beethoven Mendelssohn used the string quartet to experiment with musical forms and sound, from retrospective polyphonic and classic components to “new tones”.

Mendelssohn’s last (greater) work is his string quartet f minor op. 80. He composed this work after the shock of his sister’s death hit him vehemently and he mourning retired from the public. And in this weeks of mourning (and fury?) about the early death of his beloved sister Fanny and the premonition of his own death (he seemed to have given up his love of life) he composed this string quartet. It is a radical, highly emotional work, in its fatalistic behaviour comparable to nothing Mendelssohn composed before. It’s a first and last great eruption of Mendelssohn’s untamed (mostly negative) emotion which makes the listener wonder: This really is Mendelssohn?
O.K., Adorno’s statement of “Mendelssohn’s icy classicism” just isn’t true, Mendelssohn’s music showed emotions even before, but not like in his opus ultimus.
Some weeks after the completion of the work, Mendelssohn suffered a apoplexy and died after some days in coma.

I must say I'm only familiar with Mendelssohn's most famous works, but your post was really interesting and I think I'm going to buy some recordings very soon. Thank you.

If decide to explore the String Quartets, these are the ones I have that are highly rewarding:

Talich/Calliope/3cd set
Eroica/Period Instruments/Harmonia Mundi/3 volumes
Coull/Hyperion/3cd set
Pacifica/Cedille/3cd set
Henschel/Arte Nova/3cd set
Ysaye/Decca/3cd set
Emerson/DG/4 cdset w/Octet
Aurora/Naxos/3 volumes
Leipzig/MDG/4 volumes
Cherubini/EMI Encore/3 volumes
Mosaiques/Period Instruments/Naive/single disc

This is the set that I have. And yes, it includes the terrific Octet. The first movement of the Octet is magnificent!!! It is amazing that it was composed when Felix was 16.

Emerson String Quartet played all 8 instruments (double string quartet) for the Octet. There is a video describing how they recorded the Octet on the CD. (But I haven't yet looked at it).

Thanks for the write-up, Amade. I am not familiar(in the sense that I have not heard them more than a couple of times), but this article is a nice introduction.

I once saw this CD at a store, but didn't buy it.

Aaah...it works!
Nice to read!

I should add some good valued and good performed recordings of the mentioned works:

There are some good midprice complete recordings of the string quartets; e.g. the Talich Quartet (Calliope, 3 CDs) surely is a good tip.

For the octet (and the quintets) I can recommend the Hausmusik-Ensemble (Virgin Veritas, 2 CDs).

The piano quintet is recorded well by the Bartholdy (!) Piano Quartet on Naxos.

@ Don: I'm impressed by your list. Do you know all these recordings... or do you have all in your CD-shelf?
Can you please say a bit about your favourite recordings?
I'm interested in your opinion about the two period instrument recordings and the Emerson CDs.

Regards,
AVH.

I don't think there are great differences among the versions I listed. What I like best about the period instrument recordings are the minimal vibrato and simply the sound of the strings along with compelling changes in tempo. The Emersons are a marvel of ensemble team-work. I also have a very warm spot for the Aurora on Naxos with an intensity level greater than other groups I've heard in this repertoire.

I happen to listen to the 3rd SQ, I think for the first time. It was wonderful.