Haven't heard Villa-lobos piano concertos, but his Bachianas Brasileiras no. 3 is in effect a piano concerto in four movements (but it's not called a concerto). I don't like all of it (as a composer, he's sometimes very confusing and it's hard to see what he wants to say, at least when writing for orchestra. I like his solo or few-instruments works much better mostly), but it's got some really beautiful moments. I particularly like the first and last movement. I have a recording from EMI with Christina Ortiz on piano, she plays it very well.
I LOVE Khatchaturians piano concerto! It's wierd, but it seems to be very underrated and little known. I think it's an incredible concert, and I'd really like to play it myself.
Both Ravel concertos are outstanding. Just got the sheet music for the G major concerto, I really want to learn it.
One concerto I think is really underrated is Rachmaninovs fourth. The second movement is one of the most moving things Rachmaninov ever did. I can see why Stephen Hough said that this was the piece that almost got him to tears, because it was so beautiful. I think the first movement is really nice too, the introductionary melody is one of Rachmaninovs finest. Especially when it comes back in the end of the movement, played on strings with arpeggios in the piano...
Topic: More underrated piano concertos?