EDIT: The recurringly fantastic Equinox beat me to the punch; use her stickied thread instead.
http://forums.spiralknights.com/en/node/2021

With the return of the game, I expect that there will be a lot of demand for new recipes. Towards that goal, I thought I'd re-start the single common thread to get all the requests in one easy-to-browse location. The goal is to make it easy to tell which recipes are in demand, so that people can buy and re-sell them.

Warning: Recipes and item stats may have changed since you last played, and the wiki is not guaranteed to be accurate. Choose the recipes you request carefully, and please try to avoid "changing your mind" at someone else's expense. If you are buying recipes for someone else, remember that doing so will be especially risky until item stats are updated on the wiki.

The more we help each other find what we need, the better a job we can do at testing all the items out there!
Suggestions:

1. Give your in-game name when requesting a recipe. Otherwise, it's hard to deliver!
2. If you just purchased the requested recipe, post a quick reply so that no one else gets stuck with a copy. (name the target person AND item: "JohnSmith, I have the pie recipe you requested. Contact me from 5-8pm PST tonight")
3. For more detailed buyer/seller arrangements, use the in-game message system as a way to send personal messages
4. Once you have what you want, edit the post to remove that item. Again, this is a courtesy to other potential "recipe traders".
5. Please only post an offer for what you currently have the crowns to pay for; remember that your "buyer" has to plunk down some money up front to get that item for you.