I created a graphic design app for the iPad last year called Tree Crafter that lets you create tree inspired organic vector art and animations. It is fun to play with and quite relaxing. Also you can create great designs for web graphics or for merchandise with relative ease.
Recently I built a new web site for this app: http://treecrafter.com
If you have an iPad you should give it a go and let me know what you think. I am very keen to get it reviewed, so if you are an app reviewer, I can give you a promo code if you would like to write about it.