Cricut Access: If you own a Cricut already, you should absolutely buy Cricut Access so you have access to all of the free SVG files in Cricut Design Space. The fee for Access is annual, but there is a TON of content, fonts, projects, etc. Also, when you are an Access member, you get 10% off any non-included content AND 10% off purchases at Cricut.com.  Sign up for Cricut Access™ Standard and get 10% off all orders on Cricut.com and in Cricut Design Space™
SVGCuts.com: You will see this site features on my blog regularly. The designs are beautiful and the tutorials are helpful. I often use these files and augment them a little to suit my needs.
Lori Whitlock: Lori's designed are also featured regularly on my blog. Her design structures are ingenious, and you can count on her to make the coolest cards with features and moving parts! Sign up for her newsletter and she will send regular coupon codes: www.loriwhitlock.com
Dreaming Tree: Dreaming Tree has been active for just a couple of years, but has managed to put together quite the portfolio of projects! Their website is actually 3Dsvg.com, not dreaming tree...so a little hard to remember, but worth if it you can. Here's a link:
Lia Griffith: If you are a fan of paper decor or paper flowers, Lia's website is the authority: