Today when I was at my piano workground I encountered horn player and was forced (but eventualy it turned to be pleasure and great experience) to listen to his playing (very clearly despite two closed doors and hallway between us). Then I had conversation with other guy about french horn music and I've realised something:
French horn, at least in my opinion, has pretty weak repertoire. It's magnificent instrument with noble and rich sound but there are very little pieces for it that are real masterpieces of the same caliber as greatest violin or piano concertos.
But horns often get their "five minutes" in non-concertante orchestral music. Tchaikovsky's 5th, Mahler 5th, some Richard Strauss, Wagner (Siegfried's signal and many other short pearls).
Yay, I'm a hornist who plays a lot with orchestras so I can comment with some knowledge on the subject.
There are a lot of concerti and chamber works for horn. Not as many as for violin or piano but it is the brass instrument with the most solo music written for it. Here's a short list of great pieces:
Corelli - two sonatas
Telemann - concerto
Mozart - four concerti, horn quintet, concert rondo
Haydn - two concerti
Beethoven - horn sonata
Brahms - horn trio
Schumann - concertpiece for four horns
Saint-Saens - Morceau de Concert
Dukas - Villanelle for Horn and Piano
Strauss - two concerti
Hindermith - concerto
For great horn features in concert music:
Haydn - Symphony 31
Beethoven - symphony 3 (third movement)
Beethoven - symphony 7 (1st and 4th mvt)
Shostakovich - symphony 5 (all movements)
Tchaikovsky - symphony 4 (1st mvt) and 5 (2nd mvt)
Bruckner - symphony 9 (1st mvt)
Brahms - symphony 1 (2nd and 4th mvt) symphony 4 (1st and 2nd mvt) piano concerto 2 (1st mvt)
Copland - symphony 3 (mvt 2 and 4)
Schubert - symphony 9 (1st mvt)
Mendelssohn - Nocturne from MND
Wagner - Lohingrin, all four parts of the Ring
Schumann - Symphony 1 (mvt 2)
Dvorak - symphony 7 8 and 9 (many places)
There's lots more. This is just off the top of my head.