I think my original post about this was eaten by the robots (if not, it's lurking somewhere just out of my sight), but here's an updated list of places you can get free stickers.

I (me, personally) have actually received stickers from all of these sites, and as far as I know, they are all still operational, free-sticker-wise.

If you are outside the US, you'll want to check the links of each listing to see if they do international free-stickerage.

Also, if you are sending international SASEs, make sure to use international rate postage!

Name: Switch Magazine
SASE required? Yes. Send to:
"Sticker Dept"
Switch Magazine
PO Box 3578
Myrtle Beach SC 29578
Notes: I got a handful of pretty cool stickers from these guys. All of mine were black and yellow, with some nifty designs--all of them were different. Very cool. If you decorate your envelope, you may get more stickers.

Name: J!NX Hackware
SASE required? Yes. Send to:
J!NX
FREE Sticker Giveaway!
4186 Sorrento Valley Blvd. #A
San Diego, CA 92121
Notes: Again, you can get bonus stickers if you write them a note. (You can also get a free sticker without sending them anything by following these directions and linking to J!NX on your website.)

Name: Fantom Racing
SASE required? Yes. Send to:
FANTOM Sticker offer
50201 Silver Street
Vicksburg, Michigan 4909
Notes: I got one sheet of stickers (they weren't cut--I had to use scissors to seperate them, kinda weird.) You're supposed to specify what style of stickers you want, but the "sticker style" page that they link to isn't there, so I just wrote "no preference" on the envelope. (Maybe I should have written "pre-cut" as a style preference?)

Name:Computer Pranks.com
SASE required? Yes. Send to:
ComputerPranks.com
FREE Stickers
290 Bridlewood
LITH, IL 60156
Notes: I got six large round stickers featuring the obnoxious purple/yellow/green jester mascot. They're incredibly ugly, and I can't bring myself to use them anywhere...but they were free!

Name: Everyone Poops Bumper Sticker
SASE required? Yes. Send to:
Kane/Miller Book Publishers
Everyone Poops sticker offfer
PO Box 8515
La Jolla, CA 92038
Notes: It's charming. Really. You can see a picture of it here.

Name: BigWords.com stickers
SASE required? Nope! Follow the directions here for lots of stickery goodness.
Notes: I've gotten loads of stickers from these guys over the years. I love them.

Name: Wicked Pictures
SASE required? Yes. Send to:
Wicked Pictures Sticker Offer
9040 Eton Avenue
Canoga Park, CA 91304
Notes: If you've ever wanted large stickers featuring the logo of a porn site...this is your chance. I also got a Jenna Jameson temporary tattoo. Who can pass that up?

Name: KHCB Radio Network
SASE required? Nope. Fill out the order form at the link above.
Notes: The stickers are not particularly attractive, and the station is liable to keep sending you its newsletter.

Name: Spread The Word (Alien Resistance Movement)
SASE required? Yep. Send to:
V2/STW
Box 911
Stanwood WA, 98292 USA
Notes: SO worth it. You get over 200 stickers with a "No Aliens" logo. I also got a bunch of anti-alien propaganda.

Name: Zeptonn lab (a.k.a. stingerstyler)
SASE required? Yep. Send to:
Zeptonn
Fivelstraat 5
9715 BD Groningen
The Netherlands
Notes: Haven't tested this one out yet, but I think we can trust him. =]

Name: Velvet Chain
SASE required? Yep. Send to:
Velvet Chain free stickers
137 N. Larchmont Blvd. #535
Los Angeles, CA 90004
Notes: It looks like you have to sign up online and send an SASE. Not quite sure what's going on there. I got four or five stickers from these guys, pretty nice quality.