I have recently dedided to go to the dark side and get myself an iPhone.
Finances aside, my older Windows Mobile phone was falling appart and my service plan costs were about the same. Worth a try at least :)
That being said, I will post some of the tips and tricks that I either find online or discover myself. My first entry isn't really a tip, but just a list to a few websites which contain wallpapers compatible with the iPhone... Enjoy!
http://poolga.com/en
http://www.interfacelift.com
http://www.sciphone.net