This doesn't really fit with Anime Discussion, and it's also a poorly-concealed request to boot. It'd be better suited for either the Chatterbox (if you could provide some discussion of your own to get things started) or the Request forum (if all you can think of to say is, "What do you think the best [oekaki site] is?").
I've never found a good oekaki site. Most of the sites which are self-proclaimed "oekaki hubs" remind me a lot of DeviantArt: sure, they may have tens or perhaps hundreds of good pieces, but they have thousands of files which are pure rubbish. It's because, being an artsy-farsty site, they don't discriminate "good" from "bad" and they let everybody upload his or her own oekaki, no matter how atrocious it is.
Typically the way I find good oekaki is either one of two ways:
(a) pure, random luck in finding one particular image
(b) going to the website of my favorite fan artist and seeing if, in his gallery, he happens to have any oekaki that is drawn well
I know this isn't what you want to hear. But I don't have an answer for you, and I thought I'd write this just so you didn't think I was being an asshole with the first paragraph.
