We bought our first Prius last week and there's 1 thing I could not get over...the hideous wheel/hubcap combo. So I immediately started looking for a Toyota rim because I did not want a uni-lug generic wheel. I ran across a machined TRD wheel that I'd never seen before (on the Internet much less in real life)
They came with a very thin sidewall (25 series) that I'm not sure how long I'll be able to tolerate.
I'd read that 18" is the largest you could fit on a prius without rubbing. These are 225/35/19 and they haven't rubbed anything yet.
Here's the website I check when searching for different wheels. Wheel Size Calculator