HP has a quick and dirty little iPhone (and iPod touch) application that may interest you. It’s free, too!
Anyhow, the application, iPrint Photo [iTunes link], lets you print photos located on your iPhone (and iPod touch) on an HP printer that’s on the same Wi-Fi network. So, you’re walking about your house and say to yourself, “Man, I need to print this photo right now, well, now you can.
Being that I don’t have either an iPhone or iPod touch I can’t test it out; the reviews on the App Store are positive, though.