All links gotten from the somethingawful forums.

http://solar-center.stanford.edu/posters.html
5$ shipped
Earth Posters

www.epa.gov/superfund/kids/poster.htm
A bunch of, I don't know, water-conservation crap.

www.omega.com/literature/posters/
U.S. Frequency Allocations
Dimensionless Numbers
American Flag (only listed on order form)

www.organicvalley.com/new/cheesechart.html
It's a cheese poster. You do not fuck with the cheese poster.

www.usfa.fema.gov/applications/publ...rowse.cfm?mc=27
10 Posters on random fire safety crap. There might be dismembered bodies in some of them, I'm not really sure.

https://offers.purina.com/offer.aspx?offer=CC2K3
(US ONLY)
A free cat calendar. Not a poster, but it has cats and can possibly be stapled to the wall.

http://store.yahoo.com/apronsdirect/register.html
(US ONLY)
It's an apron. It's not a poster, but why would you possibly pass up an apron?

www.nichd.nih.gov/publications/pubskey.cfm?from=milk
Milk Posters and Stickers

www.epa.gov/espp/poster/
Endangered Species Poster

http://topex-www.jpl.nasa.gov/educa...order-form.html
(Teachers)
El-Nino Poster

http://topex-www.jpl.nasa.gov/educa...order-form.html
(Teachers)
Ocean Climate Poster

www.uoregon.edu/~program/posters.html
Homophobia Posters

www.literacytrust.org.uk/campaign/freeposters.html
I honestly have no idea, but hey, it involves Paul Oakenfold.

www.helios.gr/dis/rhodes/artgallery/form.htm
Art, something, something free poster.

[url]www.mast.mb.ca/Risk_Management/school%20bus%20safety/freeposter.htm[/url]
Manitoba School Bus Safety. I don't know. Really, I don't.

www.geop.ubc.ca/lithoprobe/public/order_poster.html
Earth-Sciency Poster. On the plus side, you can order 19 free. Yes, 19. I did.

http://lightforthelost.ag.org/light...omo-posters.cfm
Scary Religious Posters.

www.serotec.com/asp/posters&brochures/litrequest2.htm
Sciency-looking posters on apthotic things, of which I do not know anything at all in the least about.

www.co.larimer.co.us/publicworks/weeds/elkpost.htm
(US ONLY)
Weed posters. Not the fun kind, the kind in your garden. I think.

www.earthaction.org/en/02_04_chsold/response/order.html
Anti-War Posters

www.tech-res-intl.com/ose/
It's a Video and a Poster. "Women Are Scientists"

www.harperchildrens.com/teacher/newsletter.asp
A free poster and a teaching guide by Jamie Lee Curtis.

www.integritychurch.org/form2.html
A "Lord, Bless This Home" poster.

www.clueintosafety.com/cis/www/asp/register.asp 
A Blue's Clues coloring poster.

www.getfitnow.com/poster.htm
(US Only)
Navy Seal Poster

www.poets.org/npm/KitOrder.cfm
National Poetry Day Poster 

www.suzylamplugh.org/npsw/index.shtml
National Personal Safety Week.

www.llu.edu/info/prints.html
$3.50 for S&H
Really neat medical art posters.

www.nlm.nih.gov/pubs/techbull/jf97/...te.html#posters
National Cancer Institute Posters.

http://www.umc-gbcs.org/news/viewsi...php?sidebarid=1
Religious Poster. WHY THE FUCK MUST ALL RELIGIOUS POSTERS BE DEMONIC AS ALL HELL AHHHHHHHHHHHHHHHHHHHHH!

www.i1color.com/register.asp
Free posters of art stuff. They're pretty.

www.cdc.gov/tobacco/tips_4_youth/bo...efreeposter.htm
A "Boyz II Men Smoke Free Poster". Yeah.

http://popularmechanics.com/science.../4/free_poster/
SASE Required
Cool ass time-machine poster from popular mechanics.

www.cdc.gov/tobacco/christy/Free_Posters.htm
Christy Turlington No Smoking Posters. 

www.irevmodels.com/free.htm
Free poster of a bunch of models.

www.ccssinc.com/catalog/conversion_services.php
$2 Each
ASCII Data Conversion Poster

www.aaaair.com/chart.htm
An Aluminum Stringer Wall Chart. "It contains ACTUAL SIZE profiles of the most common aluminum stringers so you can order the correct material every time". Gee, wow.

www.jinjapan.org/plaza/present.html
Only 20 people are selected each month, but god damn. Japan posters / keychains.

http://www2.semo.edu/nasaerc/pubs.asp?what=1
Possibly postage, or not. I'm not sure. Maybe free.
A bunch of NASA posters.

www.niwa.co.nz/pubs/posters/
Interesting NZ maps and charts (in poster form), look around and you'll find several that are completely free.

www.discovernursing.com/prod_brochures.asp
Many, many posters with scary looking nurses on them.

www.earmedicine.com/100085.php
Free Ear Medicine Poster. It was not what I originally suspected.

www.fancyfittings.com/poster.asp
Fancy Fittings company poster.

www.healthyvision2010.org/hvm2003/materials.htm
Healthy Vision posters.

www.tcfb.com/treasure1/sample.html
(Canada Only - US has to pay SASE)
They will send you a small, paper poster with whatever you tell them your name is on it. Endless fun.

www.mcc.org/peace/resources/poster.html
Anti-War poster. Up to 4 free.

www.oandp.com/products/posimage/mailing.htm
Free Orthadonics Poster.

www.virtuelle.ca/evs/anglo/survey.htm
Free Virtuelle Poster. Some french (canadian) company, wtf do I know.

www.leukemia-lymphoma.org/all_page?item_id=83157
Leukemia poster.

OTHER CRAP:

www.enchantresshosiery.com/Free/default.asp
(Canada Only)
Free Panty Hose.

www.petrix.com/shirt/items.htm
Free shirt with a computer company's logo on it.

http://allwell.bizhosting.com/form.html
Free vitamins; from a site with lots of pop-ups. Possibly good for poisoning random children.

www.apothecus.com/dissolve2.html
I have no idea if this spawned the GBS thread with the sick man. But here's your free vaginal cleansing film.

http://dolly.ninemsn.com.au/dolly/c...petition115.asp
(Possibly only Australia)
Free tampons. 

http://tube.tfl.gov.uk/freeposter/
UK Tube Art Posters