I love chamber music, and am passionate (or insane) enough to run an annual 1-week chamber music camp (the Franschhoek Mountain Chamber Music Workshop) for high school (sometimes primary school) students. Each student is put in 3 groups, preferably with works from different periods and instrument combinations, and at the end of the week, there are two concerts for the parents/public. We generally take 40-45 students.
I start by organizing the larger groups (septets/octets), and then throw in a standard string quartet or two, a woodwind quintet, and by the time I get 2/3 organized, it becomes clear that there will be some "odds and ends" groups -- sometimes we can make standard groupings out of them, but don't have easy enough music for them. Other times there are strange instrument groupings left over. Also, for the last couple of years we have had at least one good alto saxophone player who also has to do 3 pieces. Oh, dear.
Before IMSLP, we were restricted to what was available at my university library. The "odds and ends" groups were hard to find music for. Post-IMSLP, it is still a lot of work (sometimes I have to create individual parts from a score), but the choices are endless. Also, for pianists that live far away, they can download their parts from IMSLP ahead of time and practice them, and I don't have to worry about permission to transcribe parts for saxophone.
The 2011 "odds and ends" items that came from IMSLP were:
Corrette, 3rd Concerto Comique for strings and harpsichord (from 6 Concertos, op.8 )
Dubois, Suite no.2 for 2 flutes, oboe, 2 clarinets, horn, 2 bassoons (transcribed to accommodate 2 sax players)
Kuhlau, Grand Trio in e, op.86 for 3 flutes
Kronke, Deux Papillons, op.165 for 2 flutes, piano
Reinecke, Trio in C, op.159 no.1 for violin, cello, piano (from 3 Easy Piano Trios, op.159)
The 2010 "odds and ends" items that came from IMSLP were:
Albinoni, Sinfonia in G
Bonis, Suite en trio, op.59 for flute, violin, piano
Dittersdorf, Notturno in D for 4 flutes
Glazunov, Novellettes op.15 for string quartet
Gounod, Petite Symphonie for flute, 2 oboes, 2 clarinets, 2 horns, 2 bassoons
Hasse, Concerto in F for oboe, chalumeau (clarinet), bassoon, continuo
Komitas (Vardapet), 14 Armenian Dances for string quartet
Kronke, Chamber Concerto in Old Style, op.112 for flute, 2 violins, viola, cello, double bass (we left out a harp part)
Labor, Quintet, op.11 for clarinet, violin, viola, cello, piano
Molbe, Octet, op.47 for clarinet, english horn, bassoon, 2 violins, viola, cello, double bass
If I get time, I'll post some earlier ones.