Trundle...plz Trundle....or at least a FLIPPING SKIN. GJLSDJGKLSDDKL:FJD:KL FRUSTRATION WHEN TEEMO HAS 50 BAJILLION SKINS!

Then again, Trundle needs a total rework, not just a art rework.

Sivir & Lux

I'd go with Anivia easily.
She looks so clunky.
Hextech looks good, but normal Anivia looks kinda derpy.

Sivir/karma

I'd say, in order of necessity (I've gone and looked at the various models on Lolking's modelviewer)

Master Yi (EVERYTHING ABOUT HIS MODEL MAKES ME CRINGE. His head, his feet, the way he walks, how he holds his sword, everything. He's just plain outdated on a level that is ridiculous. DEFINITELY on top of my list.)

Annie (Her model just doesn't look good at all, honestly. She's outdated.)

Sivir (Not so much her -model-, as it is her animations. Her run is ridiculous and I feel ridiculous looking at it.)

Nasus (He is supposed to look regal... but he looks like a walking bannana.)

Sion (The feet, man, the feet. Only thing really wrong with him. They're CIRCULAR ffs.)

Nidalee (Her feet, and cougar form, are silly.)

Last, but not least, Malzahar. (His pants and gloves are damnably bulky, and he could stand a few touch ups.)

This is all my own personal opinion, so I may be a bit biased.

Master Yi+rework? I tthink yesss

What about the bird?

Annie/Nidalee/Sion/Sivir. Pretty much the worst models atm.
Edit: Hell yeah, I'd buy a yi skin again if they upgraded his 90 gagillion eyed self