Great question. I use lots of patterns from Jeanette Lynton's books, Cherish, Imagine, and Reflections, plus I love Becky Higgins' sketches. I also like some online resources like http://www.stickersnfun.com/
(her sketches are a little busy, but they provide a good starting point for me). I don't know if I should toot my own horn, but I also post a sketch challenge every Monday on my blog, http://evenmorescrapping.blogspot.com/
. Hope you find some inspiration.