I used to randomly write places, but didn't start keeping track until about a month ago. Here is a list of places and their responses/what they mailed, from the past month. I wish I had the time to put in all the links, but if you just go to Google and type in what I listed, the first link contain a homepage with their "contact us" link.
If this helps you, reps would be really really awesome
Sent Frees: (all were compliments, unless noted below)
SC Johnson - Glade Candle
SC Johnson - Drano
SC Johnson - Ziploc
Sally Hansen ($5, $3, $1)
Endust
Nestle Crunch (2 frees)
Duncan Hines
Johnsonville (2 frees)
Duraflame
Avalon Organics (2 frees)
Arm & Hammer Detergent
Splenda
Sea Pak
Egglands Best
Dannon
Minute Rice
Starkist
Bumble Bee
Starbucks Ice Cream
Kashi
Reynolds
Walnut Acres
On Cor
Mama Mary's
Companies That Said NO/didn't respond..........
even though I complimented & asked for nothing :shrug7:
Clearasil (ty email only)
Huggies (ty email only)
Asian Sensations (ty email only)
Honeysuckle White
Tyson (I complained, too! My cornish hen had some gross looking feathers left on it :hectic1:)
Softlips (no response)
Pictsweet
Bounty
Texas Pete (put on mailing list, haven't gotten anything)
Purex (no response)
Kraft Cheese
Johnsons
Hershey's
Boboli
Interesting Responses/Actuals that came for compliments:
I used to use
Gillette Fusion Razors 
I wrote and complained about a pack of them seeming to get dull way too fast. They wrote back and apologized but said nothing about sending me coupons. 2 weeks later, I got a bubble mailer with nothing inside but a brand new pack of Gillette Fusion blades. I'd gotten them free (hence why I was using them LOL), and ended up with a stockpile item, finally
The easiest free was
STARBUCKS ICE CREAM! I love it. It tastes so much like Jamoca Almond Fudge from Baskin Robbins (the ice cream part, at least). mmmmmmm. I wrote and complimented them and got a free coupon really soon after.
Malt O Meal emailed me back to say that they have gotten an "unusually high amount of messages" from my area, and due to that, they are no longer offering any coupon mailings. I didn't ask for anything, just complimented them. How rude!
Splenda wrote me back to tell me how happy they were that I enjoyed their products. They sent me a free, coupons, recipes, AND 5 4-packs of Lactaid samples (seems random) and a really cute Kool-Aid spoon (a big yellow one with a smiley on the spoon part, for stirring a big pitcher of it). It all came in a big mailer.
I read on here that
Nylabone often sends free actuals for compliments. I complimented their treats and got a handful of $2/1 any product coupons. I think, if you're looking for actuals instead of coupons here, complimenting their doggie toys is better than writing about the treats.
Avalon Organics sent 2 frees that are each worth $25! The only catch is that you cannot use them online, and they do not have stores everywhere. 12/31/11 expiration date though, so plenty of time to stumble across one.
Zoe's O's sent a Tshirt and several coupons. There was no contact link, I had to Email them. Someone personally wrote back and forth with me a few times, and this is what she said they'd send. Arrived quickly!
Red Vines sent me an actual box of several licorice packages.