I was wondering whether Ravelry had an app so I could use it on my Ipod Touch. It turns out they have a mobile version of their Web site. Yeah! There are also several apps available that connect with Ravelry in different ways: e.g. Wooly gives you access to your Ravelry notebook, and Yarma is a camera app for iphone and iPad that allows you to tweak your images before uploading to Ravelry.
You can read all about these and several other knitting related apps on the Ravelry App page.