Last week's site focused on Escher products for sale. You perhaps want a wider variety in your shopping quest for gifts. The following samples web sites that offer most math-related products.
CafePress offers 58,700 different math products...is that enough. The products vary from a Pi clock to a multitude of math-phrases which can be placed on t-shirts, posters, buttons, "thongs," caps, children's bibs, tote bags, dog shirts, sweatshirts, mugs, bumper stickers, mouse pads, framed tiles, greeting cards, ornaments,.... It is a fun experience to just visit the site to read the clever phrases they have produced: "Without geometry, life would be pointless!", "How's my deriving...Call 1-800-I-DO-MATH," " "You don't scare me, I teach math," "I've counted to infinity," "Common algebra mistakes...etc.," and of course, "Math teachers make better lovers."
ScienceTeeCher provides similar products (slogan t-shirts)...but also some different things. For example, where else could you get pi-earrings...or infinity earrings? "Get Radical" baseball caps? Radical sign pin? And many Escher ties and scarves? Math cartoon t-shirts?
MathematiciansPictures is known best for its great posters of famous mathematicians (also available on t-shirts). Now, it has expanded to include special focus items related to pi, the godlen ratio, and physics. For example, they sell the "World's Largest Pi" posters (4 ft x 8 ft)...a 31.4 feet scroll poster of pi's digits...some weirdness (πKong and πZilla)...and πcertifed Geek products (or even Phi-certified or e-certified).
The ProudNerd site has a special section for math folk. It offers many t-shirts not found at the other sites. At this rate, I think you could wear a different math t-shirt every day of the year! If you don't want the slogan on a t-shirt, you can get sweatshirts, dog shirts, boxer shorts, caps, bags, backpacks, mugs, buttons...an unusual "Affinity for Infinity Teddy Bear." The sites motto: BE PROUD TO BE A NERD. WE'LL HELP YOU SHOW IT OFF.
Acme Klein Bottle offers the more usual gift...that of your personal Klein Bottle....a three-dimensional surface whose inside is the same as its outside....or if you can visualize the edges of one moebius strip (left twist) glued to another mobius strip (right twist)! Many sizes are available, including a GIANT 1-meter tall bottle for only $12000. And if bottles are not your thing, you might be interested in buying a Klein Bottle Hat or a Mobius Band Scarf.
Proactive math teachers might casually mention/show the above web sites to their students, possibly planting some "seeds." Or, to take a less expensive road, you might show them the web site How to Make a Gift for Your Math Teacher
. Every math teacher needs 100+ versions of the "Golf-Tee Puzzle."