I use Society 6 and they have good quality. I know of people who use Zazzle as well but I don't have any experience with them. I keep my account on there to produce things I can't practically make myself for cheap, like shirts, rugs, clocks, large canvas prints, etc.
But like with all of these types of sites where they print your design on their own supplied product and they fulfill the order for you, the margins will be low and you likely won't see much money unless you're selling a LOT.
I've found more success in opening my own storefront through Gumroad and Storenvy. These sites are like Etsy, where you have to make/find independent producers to create your items, keep your own inventory on hand, and pack/ship out the orders yourself. Sure it's more work, but you get higher margins. If you want to sell small things like charms, pins, and stickers, this will be your best bet.
A note on the sites listed in the post above:
Big Cartel works the same as Storenvy and Etsy, but I believe they have a maximum amount of items you can list unless you pay monthly. (Gumroad, Storenvy, and Etsy are unlimited as far as I know).
InPrnt requires an application or an invitation from an established artist on the site before you can make a storefront with them. They are curated by the staff/community.
I'm pretty sure some of those T-shirt sites have an application process as well, but I don't have any experience with them so I can't say for sure.