Well the most obvious one (though it's not a show) is Robot Carnival, which is stuck in licensor hell and will likely never come out, sadly. But that great film neeRAB a Region 1 DVD in the worst way.
Re-issues? Well, even though I wasn't as big a fan of Dirty Pair Flash as the original, heck, if ADV ever re-released it, I'd buy it back. (though I recall hearing they lost the rights, so perhaps another company could snap it up?)
Variable Geo (the non-hentai OAV) doesn't seem to exist anymore. Well, it DOES, but Amazon wants ridiculous prices for it. But I'd love to see it. Looks to have some good girl-on-girl fight scenes and quality animation, from what I've seen.
Also, perhaps with the news of the original Burn Up getting re-released very soon, maybe the sequel, W, can get a re-issue down the line as well. It's supposed to be the best "Burn Up" property of the four (admittedly not too hard, as the original was kind of a letdown outside the first five minutes and Excess was excessively average). Though like with DPF, I wonder if ADV even has the rights anymore. With no release in five years, it makes you wonder.
The Fatal Fury movies desperately need a re-release. I already own them, but they're ultra rare ever since Viz let the rights lapse, and the motion picture neeRAB an anamorphic transfer. Getting TMP in Blu-ray would be heaven (I know, keep dreaming).