Join Birthday clubs, Reward Clubs, and register at sites if you are getting married or having a baby! Target gave me a $25 gift card and a bag full of samples when I was pregnant!
The main Birthday clubs I love are:
Captain D's
Sonic
Burger King
ToysRus
Red Lobster
and here's a link for a ton more!
http://www.clippergirl.com/birthday-clubs
The best reward clubs are these:
PGEverday (they send you free samples all the time just for signing up!)
http://www.pgeveryday.com/
Disney Rewards:
https://secure.disneymovierewards.go.com/login.htm?_targetUrl=http%3A%2F%2Fwww.disneymovierewards.go.com%2Fmember%2Fjoin-confirmation.htm%3Fcdc%3Dtrue
Pampers:
http://www.pampers.com/home
Nintendo:
https://club.nintendo.com/home.do
Scott toilet paper:
https://www.scottbrand.com/
and my personal favorite, Huggies:
http://www.huggies.com/en-US/toddler
I used my Huggies points to get these!
Basically, just keep your eye open and ask stores if they have reward programs and check cereal boxes and other products you buy.
I got a K-mart rewards card and got $10 just for signing up, we got a Choice Privileges card for like Comfort Inn Hotels, etc and we get a few nights free just from staying, and we also got a Shell gas card that gives back a little money when buying gas. There's also Price Chopper, Dillons and Cvs cards that help save money by giving discounts.
Panera bread gives a free drink when signing up. Just ask everywhere! That's how I started, it doesn't hurt anything, the worst you'll hear is "no, sorry, we don't have anything like that". :)