HP has a new product called iPrint Photo (click opens iTunes) available in the App Store that makes it very simple to print your iPhone pictures. The free download opens to a list of photo albums that looks very similar to the list in the Photos app on the iPhone. Tapping on a photo brings up a Print Photo page with a large Print button on it (see photo at right). If you only have one networked printer available, just tapping the Print button sends a 4x6 inch (10x15 cm) print job to that printer.
If more than one HP inkjet printer is on your local Wi-Fi network, tapping on a printer search icon brings up a Chooser-like list of printers that you can select one from. This is an excellent free app -- it took no setup and I was able to print a picture immediately after downloading the software from the app store.
Between this software and HP's announcement of their Mac-compatible media server, it looks like HP is starting to play nice with Apple!
Check out the gallery below for a few more photos of this app in use.