Land Raider, Corvus Blackstar, Baneblade (and variants), Drop Pods (though I would prefer rules for Roks instead).
To be honest I hadn't even thought about the Baneblade and variant looting. Anybody know if we still have access to the Skullhamma, the Orkified Baneblade from the original Apocalypse 40k book, or was that squatted?
As for Roks, maybe its me, but the fluff for Roks NEVER sounded like Drop Pods to me. Yes they are asteroid weapons that are 'dropped' from orbit, but in the fluff of Armageddon when they first showed up, they were utilized more as strongholds armed with Tellyporta arrays and gobs of weapons instead of a mere delivery system like a Drop Pod. To me, a proper Rok would be a Fortification with automated fire weapons like a Bastion PLUS let an Ork unit within 6" to be removed from the table and deep strike anywhere on the board AND/Or allow Reserves without the Deep Strike rule to arrive within 6" via Deep Strike without scattering.
My personal favourite was the ability to loot imperial war gear for my meks. Being able to take a graviton gun to bring a building down around some marines always made me laugh maniacally.
Where was I for that?! Seriously, I don't remember a way that we could steal grav guns.
Looting a knight would be sick. I actually saw a converted ork knight on eBay a few weeks ago and it made me drool.
Now why didn't I think of that? Looting knights....
We technically can take Imperial Knights, we just have to keep the Orks and the Knight 12" away during deployment (and ideally 6" away during the entire game to avoid One Eye Open). A relatively easy thing for Trukker armies, not really feasible for Footsloggers though. I'm not proud of it, but I've contemplated scratchbuilding a Knight Crusader. Haven't built it because I'm still so personally opposed to Knights and I'm also not generally for any model that is almost 1/4th the points of my game.
After being asked to brainstorm some conversion ideas for how to scratch an Exorcist tank, I'm actually wondering why we don't see them more often. Sure the SoB or Soritas army is an unsupported joke, but the Exorcist tank is actually really solid and that randomness without [obscenity deleted]-ness is something I miss about Orks.