There are tons of cuts that have since only come out on recent reissue labels (e.g. grapevine), I think the thread would probably be best confined to older reissue labels from the 60s and 70s. Either way, this is a cool thread, I don't have anything to add as the ones I knew were mentioned already, and there were a couple mentioned that I didn't know.
Actually, I just thought of a random one -- there is a bootleg label "red rocket" out of pittsburgh that bootlegged a bunch of chicago stuff (ideals, duvals, etc.) in the 60s. But there is one northern record on the label that only came out on that label -- the Stylers on red rocket. So I guess that's a legit release on a reissue label.