Oscar Blume’s 12 Melodious Duets for Trombones, Baritones, or Bassoons is a wonderful pairing for his trombone etude book. Both are technically challenging while being idiomatic and comfortable on the instrument, as they were originally composed specifically for the trombone.
I consider these to be “concert duets” because this title includes a separate book for both trombone 1 and 2. This generally means they are meant for concert performance where each performer would have their own stand. These work equally well on recital programs and the studio, and should be a staple in every player’s collection.
Check out the first page of each book in the samples, then grab an immediate PDF download above.