A few monsters from the classic series that made it into the last Doctor Who RPG but haven't reached the revived series, Classic Who action figures or the hearts of the nation.
Draconians are basically green Samurai. In space. They'd need some work to make them distinctive from a cultural stereotype, but it's nice that there are non-monster aliens out there. Still, the role is partially filled by Silurians (especially now) and Ice Warriors.
If I brought them into the new series, I'd probably borrow some of the look from Scarrans on Farscape to make them look a bit less like, well, the new Silurians. And do something about the "Samurai" thing as well - we have adventures in medieval Japan for those.
A sign of Time Lord being from the early wilderness years, the Haemovores from The Curse of Fenric are a fine enough bunch of rugose submarine vampires (more Lovecraftian than the Sea Turtles) with the ability to weld metal for no readily apparent reason. They largely work as-is if you need icky vampires from a polluted paradoxical future. I can imagine their hellish future Earth could make an interesting backdrop for an adventure, but not exactly a barrel of laughs one.
Robots designed on the Dalek model but as Kim Newman puts it: "The Mechanoids missed so widely that they didn't even return in the mid-1980s". One has actually appeared in the new series, though, before the Daleks even! Missed it? It was in the establishing shot of Van Statten's museum in Dalek. ... Yeah.
They'd do for background creatures or blatant obscurantist nostalgia kicks.
A race of beautiful androids who care nothing about humanity but instead want to wipe out the Daleks? Now this I could find a use for. I'd lose the Rick James outfits, though. It would make passing for normal people a lot easier...
Looking like Next Generation Klingons going undercover in Planet Of The Apes and acting like Orks from Warhammer 40000, they make good goons either silent and serious or noisy and comedic. But Who tended to go for variety here, so the henchthing-for-Daleks role has also gone to the likes of Robomen and most recently Pig Slaves, and nowadays Daleks can get up stairs so they need knee-having help that bit less.
Those new Silurians have ripped off their best trick too. Poor sods.
Determined to come last in the Who monster alphabet, we have yet more shapeshifters whose natural forms are twitchy-nosed banana-people, and who need to keep the people they copy alive to renew the template every two hours... so they're rubbish shapeshifters then. Still, the "keep the people they copy alive" bit allows for a bit of tension with hostages and the like. Of course, the Autons borrowed that. Cheeky Autons.