I am very fond of chamber music (more so than orchestral or piano, typically). Cello Sonatas I've appreciated (not counting sungs like Prokofiev, etc.) include:
masterworks:
Röntgen (Bb, a, g, c, b, D, f#, d, e, c, d, a, c#, C), particularly 2, 5, and 7
Thuille (d)
Reinecke (a, D, G)
Novak (g)
Myaskovsky (D, a)
Magnard (A)
Lekeu (f)
Grechaninov (e)
Franck, Eduard (D, F)
Foerster (f, c) - I have the f minor, but not the c minor (yet)
Alkan (E)
Other good, (generally) tonal sonatas:
Zemlinsky (a)
Weinberg (C, g)
Stanford (A, d)
Schumann, Camillo (g, c)
Scharwenka, Franz (e)
Scharwenka, Phillip (g)
Rubinstein (D, G)
Ries (C, A, g, ?), I only have 2 and 3, I'm fond of 3
Reger (meh) (f, g, F, a)
Rawsthorne
Pfitzner (f#)
Moscheles (I have No. 2 in E, Op. 121, but I can'/t find reference for "No. 1")
Kodaly (op. 4)
Kabalevsky (Bb)
Ireland (g)
Hummel (A)
Hindemith (op. 11/3, E)
Herzogenberg (a, D, Eb)
Henselt (b)
Goldmark (F)
Goens (no sonatas, but lots of cello and piano miniatures)
Fuchs (d, eb)
Franck, Richard (D, eb)
Enescu (f, C)
Dohnanyi (bb)
Delius (1916)
Bridge (d)
Bowen (A)
Biarent (f#)
Berwald (Bb)
Bennett (A)
Barber (Op. 6)
Atterberg (b)
Sonatas I would like to hear
Ropartz (g, a)
Raff (op. 183)
Parry (A)
Onslow (Op. 16)
Lachner, Franz (A)
Juon (op. 4, 54)
Jongen (op. 39)
Jenner (D)
Gernsheim (d, e)
Draeseke (D)
d'Indy (D)
Brull (d)
Bortkiewicz (op. 36)
Bax (Eb, D, f#)
Bantock (b, f#)
Balfe (Ab)