What are some of your favourites among the lesser-known Piano Sonatas? I've really taken a shine to No. 5 in C minor, Op. 10/1 and No. 12 in A flat, Op. 26.
Op. 26 is a great favourite. The first movement is among Beethoven’s most delightful theme-and-variations creations. If I remember correctly, it was also a favourite of Chopin.
I’m also very fond of (in no order of preference) Opp. 22, 2/3, 28 (is it considered lesser known?), 101 (again, if it can be considered lesser known), 90, 2/1 (imagine my joy when I heard it being played a few years ago at Capodimonte Museum in Naples out of the blue - there was a pianist playing a concert grand in one of the state rooms and music was echoing throughout the palace: Scarlatti, Chopin… and the finale of Beethoven’s Op. 2/1). I assume none of the magisterial last four sonatas is considered lesser-known territory. The infectiously fun last movements of Opp. 81a and 31/3 are also great favourites.