I am not going into the uncommon/rare/obscure/elusive discussion
Some of my favorites:
Moscheles, No 6 and 7
Vianna da Motta, No 1
Arensky, Op. 2
Glazunov, No 1 and 2
Cramer, No. 8
Rautavaara. No 1 and 3
Reger Op. 114
Liszt, 'Malédiction' S121
Hummel, No 1-3 plus the concertino
Respighi PC in A Minor
Thalberg Op. 5
Kullak Op. 55
Dussek Op. 22
Swarwenka No.3 and 4
Fuchs Op.27
Most of them all sound the same, though. You wished some of them would be a bit more imaginative and modern.
I also recommend the Medtner and Barber concertos to the people who haven't heard those..
I would like to hear the other Busoni concerto. Plus I bet one of those eight Sorabji concerto's is fun, but I have heard none. Ooh and maybe I'll add some late.r