I also really love Stashbot. While this app is not free, it is reasonably priced and worth the money
Lastly, one of my favourite iphone/ravelry features is yarnphone.com. I have literally used this all over the continent. If you are travelling and use an iphone, go to Safari, type in yarnphone.com and yarn stores - complete with addresses and directions will appear according to your location. This is an innovation by Casey at Ravelry. It's like a little bit of magic on your iphone.
If you have any amazing knitting apps that you would recommend please put them in the comments.