Hard to give a list of pieces unless you tell us what kind of pieces you want to perform 
The main reason for the concerts to is give my friend more solo-stage experience. He got his Master for cello not long ago in the Royal Academy in London, so technically he should be allright, but they dont do much to get somebody more solo experience.
The pieces i'm looking for are supposed to be nice to hear for a broad audience, but we're mainly playing them for ourselves, the fun and the money is nice too ofcourse

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Thats why i like pieces like the Rachmaninov sonata so much; technally challenging enough but not too hard, musically very nice for both cellist and pianist and good for a broad audience.
Btw, we still both enjoy playing 'the Swan' alot, it should be definitely somewhere in the top of the 'most beautiful cello pieces-ever'-list, but the piece is too damn cliché to perform anywhere :p
Gyzzzmo