Last summer I played a flute/piano recital with a neighbour at a retirement home--an amazing experience, and I actually ended up carrying at least 80% of the performance but then I actually had time to practice, whereas she's 40-something and only has time for on-and-off stuff.
Anyway, I just have to push the Bach sonatas for flute/piano. We did the first one in B minor, and it was a little challenging, especially the demanding 1st movement (which is quite lengthy) and awkward 3rd movement. However, even though I am not even a very good pianist myself, I got by fine with one or two slipups (after all, in such a scenario, sheet music is always acceptable for both players). Interpreting the piece was ALWAYS a blast, though, and every time she came over I'd hurl tons of new ideas at her about tempi, rhythms, ornamentations and so on. Unfortunately, she was more of a conservative player from the old days and only saw Bach in a sort of black-and-white way, so we didn't get the somewhat Gouldian excitement that I had been trying to build (sort of), meaning that we didn't do anything "unexpected" or...well, you get the idea.
But that's neither here nor there. Try any of the sonatas. I played through the one in Eb by myself and absolutely adore it. None of them are too hard as far as the accompanist part goes, but since the instrumentation was different in Bach's time, modern flutists frequently, according to my neighbour, run into breathing problems given the drawn-out phrases with few rests.
We also played an arrangement of Ravel's popular "Habanera" (sp? ugh I can't think), a movement from a classical sonata by someone whose name narrowly escapes me now, and even a Gieseking sonatine in Eb minor if I remember correctly--that one was a little more challenging but not too far a stretch. I believe we also played an arrangement of a John Field nocturne and then she played a Debussy something or other by herself; I did the rest!
It was magnificient. I'll let you know if anything else pops up! You might try looking at Faure and Franck; I do believe they both have comparable flute sonatas (could be wrong) and although I have neither played them nor heard them, I'm sure they must be worth looking into at least.