I will say real quick to be careful of who you join and to research them. Lots of places can offer a lot and if you fall for it and give your info it's too late to turn back. Google the name and add things like "reviews" or "scam" after it and read what pops up. Here are some sites that you can join, that I personally use.
There are other sites that I have joined that give out samples and even full size products. You just join and sign up when they are giving out the samples.
There are other random sites I have joined where you have to do simple tasks to get your "points" to cash in.
HitPredictor- This is a site where you hear clips of new songs and rate them. They have sent numerous emails(not spam) offering me to rate a certain amount of songs in a certain time frame. I've gotten at least $20 in Amazon gift cards from them in about 3 months.
Recyclebank- On this site you can take various quizzes about being environmentally friendly for points. You can redeem your points for various things. I've gotten 4 magazine subscriptions and 3 coupons
Crowdtap- Here they give you simple questions to answer and also ask you to rate a page they show you. When you get the rating option, you just have to get 4 other people to rate and they will pay a $1. I welcome your page links on my facebook page if you need help with these. It's easier than it sounds and once you reach a balance of $10 you can cash out for an amazon gift card. They also take a small percentage and donate it to the charity of your choice. I've received $20 in Amazon gift cards
SwagBucks- I mentioned this site earlier because on Fridays they give etra points. Here you get points for using their search engine or getting "swag codes." They have other options like games, videos, and offers vut I just do the search and codes. I've gotten a $5 Amazon gift card