A lot of the stuff I get for free are from review clubs! All they want is an honest review on amazon (and if you have a blog or youtube channel like I do, that helps too!) Here are some of my faves. If you sign up through my link, we both get rewarded!
Elite Deal Club - Steep discounts and occasional freebies, mostly beauty and health products. Check every morning at 10am ECT!
AMZ Trader - Highest recommended, easy to use. They have everything in every category.
AMOne Review - Same interface as above, easy to use.
I Review Home - Limited products but still a great website
Reviewer Group - Great interface, helps you keep track of what you've ordered.
No Kidding Coupons - Mostly coupons for discounted things rather than free. Some great stuff, a lot of health and beauty products, some home goods and baby products as well.
Product Pilots - Login through Amazon makes it easy to join. Mostly steep discounts rather than freebies.
Amazing Deals Group - I'll be honest, not my favorite, but they occasionally have some good stuff. Mostly discounts, few freebies.
Snagshout - Same interface as AMZ. You can also check off the "only Prime" box so you know if you'll get free shipping.
Tomoson - A little harder to get approved for stuff, but once you get a good rating you can actually start getting paid to write reviews and promote items. It helps to have a good social following first. Some companies require you to have multiple social networking sites just to apply.
Deal! Go! Go! Go! - Similar interface as AMZ, definitely managed by non-native english speakers, but works fine.
MusicEver heard of Noisetrade? Artists put their music online to become better known. Sometimes I review the music here.
Podiobooks is great for self-published, indie, or obscure audiobooks. It's also great because you don't have to download the whole book; you can subscribe to it and not fill up your hard drive -_-
Learn Out Loud
Learn Out Loud had lots of audiobooks, and some are free. Here's the freebies page.
Open culture has a lot of classics. Here's a list of freebies (sorted in alphabetical order).