This is an old post but here's my 2.5 cents: I found that the Story World create-a-story cards kit by Templar Books (by John & Caitlin Mathews) works well for coming up with quick and dynamic ideas that can be quickly adapted into random Grimm encounters and even developed into full-length stories and sagas. If you are comfortable running encounters on the fly (Grimm is really easy to do this with without a lot of detailed narrative or even story logic) these cards can be used as a "Random Monster" or challenge deck. They provide a unique visual element and can even become the focus of being magic items themselves. There are several themed sets of cards from the basic kit, Fairy Magic, Haunted Houses, Sea Legends and (entering the realm of Narnia perhaps…) Christmas stories. They are relatively inexpensive as well (about $10) per set. Each card has a bunch of visal elements that tie in to other cards so it helps promote some sort of story continuity. Good Luck.