Go here to send an email to P&G about Venus razors - I received a pack of razor cartridges.
Go here to send an email to Hefty - I received a coupon for a free Hefty product of my choice (we all know how expensive good quality trash bags are).
Go here to send an email to Bayer about Aleve - I received a coupon for a free product up to around $18 (if I remember correctly - I got this ages ago).
Just FYI: I created an email address just for coupon stuff and that's the email I give to these companies when I fill out forms - just so it won't junk up my regular email. I wouldn't give a fake one because sometimes the coupons come through email, not snail mail.
Also, if you're wondering what to write, I usually just write a couple of sentences. For Venus I probably wrote something like "I just wanted to take a moment and let you know how much I love Venus breeze razors. It's such a time saver to not have to worry with shaving cream in the shower. Thanks for what you do!" Just make sure you mention the actual product so it doesn't sound too terribly fake.
Let me know how it goes!! I will try to start doing this every week or so.