I'm not 100% sure but I think
- The other green goblins
- The other Hobgoblin e.g Jack O'Lantern
- Lady Ock
- Grey Goblin
I'm sure there is more I just can't think of any with out saying people like White rabbit
Some of those characters are redundant, do we really need another Goblin at this point? Two is enough. Perhaps Roderick Kinglsey can play a different role in the UU (Mackendale sucks though). Ultimate Demogoblin seems completely pointless. We already had an Ultimate Kaine in the Clone Saga (the deformed Parker clone). Lady Ock is also redundant, she is just a female version of Ock, instead of being her own character. Carolyn Trainer should have a different role in the UU. Scream she is a non character, she barely had any stories or development in the 616 universe, also there quite enough symbiotes in the UU at the moment. Morlun, nah, no magic Spidey in the UU and without magic he is just another vampire villain, again already done. Hydro man is just the poor man's Sandman.
So lets look at the villains who aren't just copies of more popular characters, ones that have potential. Symthe could be interesting, they could do an Ultimate spider slayer invansion story, he can just reprogram some of the spider slayers SHIELD has made. Chameleon could be interesting, unless Bendis intended the guy pretending Spidey to be Ultimate Chameleon, which would be lame. Plus it doesn't seem like Bendis likes villains who rely solely on cleverness, so we may not see an true Ultimate Chameleon. Tombstone could be interesting, as well as Shriek, Shriek there is a lot that could changed, but I'm not sure how an Ultimate Tombstone would be different from his 616 counterpart. Jackal I hate on princiapl and it will take a lot to get me to like an ultimate verison of the character.
Now ultimate White rabbit could fun, because she is supposd to be a joke villain, so Bendis could use her in a silly way and no one would mind. Heck Ultimate Legion of losers could be a fun one shot.
Now perhaps USM could borrow from other rogues galleries because there are a quite a few decent B-list DD and Iron man villains who won't be introduced in the UU otherwise. Here some examples:
I think say, Blizzard, could work as a USM villain, its not like he is getting to the UU any other way. Also we haven't seen beetle intoroduced to UU proper (video games don't count).
Or Bendis could expand upon some of the villains he has already introduced (Electro, Sandman, Vulture have never gotten thier own arc.)