There are a few still awaiting proper reissue:
A Drum Is A Woman
Peer Gynt Suite
Nutcracker Suite
Suite Thursday
Bal Masque
Jazz at the Plaza
Most of these were on French CDs, but all deserve the definitive treatment.
I think the three suites are still available on a cd called "3 Suites". Bal Masque was issued without the fake applause as part of the Sony '51-'58 box set. But it would be great to see Jazz at the Plaza as well as a collection of all the singles he did for Columbia after '49. (I've never even heard The Asphalt Jungle Twist.)
I'd also love to see a cd reissue of the entire Gil Evans at the Royal Albert Hall. Part of it was on an RCA Lp and the rest of it on Mole Jazz and none of it has been on cd as far as I know.