So I had an idea and tried it out, and lo and behold, the iPhone optimised version of Deviantart.com worked nicely on my 5800! Take a look!
So I tried out some other iPhone optimised sites too, here's some screenshots:
Amazon: amazon.com on the mobile browser
Fox News: iphone.foxnews.com
Unfortunately Apples iPhone Webapp page won't even load up on the built in S60 browser so no chance of using those. Some of these sites are good enough though! Let me know if you find any more worth adding.