Here are two great tips for designing good looking web pages for iOS devices.

Targeting the iPhone 4 Retina Display with CSS3 Media Queries
All iPhone OS 4 devices report the same user agent. This article explains how you can detect the high resolution display on the iPhone 4 and adjust graphic detail as needed.

Targeting various iOS devices with media queries
This article explains how you can add separate icons for each iOS device for their home screens. Check it out if you want bookmarked pages to look good on the iPad and the iPhone 4.