You can now indicate what recipes you know on our new Recipes page. Eventually that link will work =)
Until then, login and head to your member profile page. Follow the link to the tradeskill in question (e.g. alchemy) and it will let you mark off what recipes you have (or don't have).
If you keep this up to date I'll keep my eye out for recipes members are missing. If you don't update though, I won't be buying anything for you!