With some of the holiday cards I send out this year, I included a plastic snowflake ornament that I printed on my 3D printer. Granted, a relatively flat ornament is not the best design to show off what a 3D printer can do, but it is one that fits inside a holiday card envelope and doesn't push the weight over the 1-ounce mark.
If you're not familiar with 3D-printers, you could look up the dry Wikipedia article that looks kind of boring and technical, or your could check out this sweet time lapse of a Yoda bust being printed in green plastic. Basically, it lays down very thin (less than 1/3 of a millimeter) layers of melted plastic until they build up to something.
I built the printer from a kit that I got about a year ago, with all of the metal rods and motors and a ridiculous number of nuts and bolts. After two weeks of building the printer, several months calibrating it, forgetting about it, getting too busy with work, fiddling with it some more, printing out cute (and functional!) tiny alligator clips, jamming the print head, and fiddling with it just a bit more, I'm finally getting it close to useful.
As you can tell, 3D printing is probably not yet ready for the average home user. But if you like to fiddle with mechanics, robotics and electronics, it can be a lot of fun. The finish on my prints isn't quite perfect yet (still needs more fiddling), but it's getting pretty close.
So, this holiday season, I went to Thingiverse, which houses tons of free models that other people have created and uploaded for you to print with your printer, downloaded a snowflake ornament, and modified it a little bit. And then the printer went to work.
(Warning, this video, though a time lapse representing over two hours of printing, is still 7 minutes long and kinda boring, but if you want to see how your snowflake was made, this is it! I recommend watching a little bit at the beginning, and then skipping to about the 6-minute mark.)
And then I stuck it in an envelope with a link, and maybe you typed that link into your browser, and here we are. Enjoy!