The Crochet Life: Trying New Yarn.

I've been wanting to try handmade online yarn. I normally purchase from Michaels', Hobby Lobby or even Walmart. I've been wanting to expand my yarn collection (you can never have too much yarn) to see what's out there. I've seen numerous hand dyed and natural yarn out there and I really want to get my hands on them.

When I started crocheting, my go to yarn was Red Heart. Hey, it is inexpensive and quite perfect for starting/testing new projects. With the accessibility of store bought yarn I have always been a bit curious towards handmade yarn particularly online. So what's stopping me? I'm honestly quite perplexed as to where I should start and what I should look for. 

So! Here is my question for those who hold an adoration for the fiber arts: 
What are some of your favorite online stores/places to purchase hand created yarn? 
I'd love to hear others' input or any other advice regarding yarn!