If you just stick to Reishi, Chaga, Morels, Chicken-of-the-Wood, and Puffballs you can't go wrong. Easiest to identify and only the morels and CofW have a look-alike. But it's easy to determine. Morels, once picked, you see if the stem is hollow. CofW, you can tell by the bright yellow color. The look alike is more brownish but not poisonous, just doesn't taste good.
If you see a large black horn-like cancer looking growth on a birch tree, thats a chaga. It along with reishi are the two best medicinal fungus you can get. Reishi grows on dead hemlocks and you can't mistake it for any other shroomage.
I think you just made me want to brew up another batch!
Happy Hunting!