The iPhone has a great useable web browser and has been designed from the ground up to give a good web experience. However there is still a place for fast loading, lightweight, mobile web pages.
Here are some of the ones on my iPhone.
www.bbc.co.uk/mobile – Mobile site from the BBC – my favourite mobile website – with content choices and a “My Location” feature
www.bbc.co.uk/mobile/click - Click the BBC’s technology news programme
www.bbc.co.uk/mobile/iplayer – Streaming BBC content to your iPhone
touch.whatsmyip.org/ - as it says, it will return your internet ip – with extra network tools
m.guardian.co.uk – more news and articles from The Guardian newspaper
iphone.tvcatchup.com – you need to register (for free) for streaming TV
http://gpscoords.cinnamonthoughts.org/ - this is a web app, it returns your GPS location
en.m.wikipedia.org – Wikipedia for a mobile device, although there is an app for that!
www.rspb.org.uk/mobile/ – indentifies 117 British birds
http://m.fanfiction.net/- Fan Fiction site. TV, films, books all types of genres. If you look around there are some really good stories here.
eBooks on the go – you will need to install an eBook reader for epub books and then you can choose to download epub books from these sites to your iPhone.
http://m.gutenberg.org/ – a fast way to navigate the Project Gutenberg web site.
http://m.feedbooks.com/?format=mobile - FeedBooks catalogue.
http://www.munseys.com/mobi/ - Munseys collection with a vast range of pulp sci-fi.
MegaReader has access to FeedBooks and Project Gutenberg built in – you would have to add Munseys.
If you have a WordPress site you can optimise for use on a mobile device, using the same content as the full site, the web site detects the browser used to access it and will present to a mobile browser a mobile web site. I use the free WPTouch plugin on all my self hosted WordPress sites.