Something that's been bothering me lately.
Almost every piece in the classical repertoire has at least one movement in duple time (i.e. 4/4, 2/4, 2/2, more rarely something like 4/8). It's not extremely uncommon for a work to have all of its movements be in 2 or in 4, even if it is a very long work (examples: Mozart Piano Concertos 20 & 21, Beethoven Piano Concertos 1 & 4, Bruckner 4 revised version, Elgar Symphony 1 & Violin Concerto, Rachmaninov Symphony 2). But it seems to be extremely uncommon for a work to have no movements in 2 or in 4 (the only pre-20th century example I can think of right now: Alkan's Concerto for Solo Piano). Does anyone know of additional examples?
I'm excluding collections of pieces that can all be played individually, which is why a set of waltzes or other dances wouldn't count (or likewise a collection like Godowsky's Triakontameron), unless it was specifically written to be played as a set (e.g. Ravel's Valses nobles et sentimentales).
(Some other 20th century examples would be Prokofiev's Piano Sonata No. 7, Ravel's Piano Trio & not that many others before one starts to get into music which departs entirely from the idea of a consistent metre.)