You may not have noticed, but the Web is crowded with sites that feature paper models you can print out, cut, fold, and glue together! Here's a small sampling—some might prove useful as an addition to a project, or something...

• Trouts and Seasons of the Mountain Village
  Realistic fish models to make and, um, stick on your wall, or something! There's also a second page.
• Canon Papercraft
  Canon has a variety of models to encourage you to use up that expensive printer ink you might have bought from them! Some of the categories, like science, buildings of the world, and costumes of the world might be especially useful for school.
• Yahama Motor Company
  Believe it or not, Yahama has quite an offering of challenging, realistic-looking models, featuring motorcycles and rare animals.
• Life is Art
  Excessively cute, stylized models at this Japanese site—animals and vehicles. (I've got their boxy-head monkey sitting on a shelf near my computer, because he's cool. No, shut up. He is.)
• Chao Laboratory
  A few simple and colorful models, featuring a pretty cool-looking penguin and gorilla. But the tour-de-force? Papercraft karate tournament! I'm not sure how this works exactly, but there are instructions: Beat the predetermined position of the ring with your finger and make your CHAO fight against others! Pushing out from the ring or make it fall down will be your victory! Looks like thumb-wrestling has finally met its match.
• Flying Pig
  Very high-quality, animated/mechanical paper model novelties. These are really cool, and most cost a few bucks to download. You'll also find sections about technique and engineering, where you can learn more about creating paper machinery. There are a couple free downloads, as well.
• The Toyshop
  Ravensblight(?) offers up some models best-suited for Halloween, but some, like the medieval helmets and Splatterbot are never out of season! (And Halloween or not, who doesn't get a hankering for a good game of undead chass every now and then?)
• The Toymaker
  Quiet and simple models, reminiscent of early 20th century designs and motifs. Features several types of containers that some of you might find useful, even though you're probably too old for a Tooth-Fairy gazebo. Maybe for a little sister?
• The Best Paper Airplane in the World
  No explanation needed, I'd imagine. Just remember who showed this to you, and keep them out of my room! (Once you've mastered the folding, you can download and print some custom designer sheets from the site, too.)
• Aliens Papercraft
  Several models inspired by the film, most notably a full-sized M41-A Pulse Rifle composed of over 200 parts! There are also some bonus models from other sources.
• SF Papercraft Gallery
  An incredibly detailed Lens Head and Gun Walker model, plus stuff to gawk at in the gallery.
• DNA
  Paper DNA strands in three sizes, one suitable for Coke-bottling, it looks like.
• Map Fold-outs
  World maps printed on various polyhedra; everything from simple cubes to rhombicuboctahedra(?!).
• Robots!
  More crazy robot models than you can shake a katana at, all in Japanese. Give the page time to load; it's long. After that, the best I can tell you is that clicking 写真を全部見る near each model will take you to a picture of the completed robot, and clicking 型紙はコチラ will take you to its corresponding download page. Good luck!
• Robot Papercrafts
  A Japanese page with an assortment of angular models.
• Howl's Moving Castle
  An incredibly detailed model from a Studio Ghibli film (the parts come in a 26-page PDF file!), you'll need to have some time on your hands to complete this one. The link above goes directly to a download of the 50MB file—don't click it unless you mean it! (Here's the American site for the film, if you're interested.)
• Master Chief
  A pretty bare-bones model of Master Chief from Halo—maybe stand it next to the 'ol Xbox for inspiration or something. There are no pictures of the completed model, so I'm not sure how good this one is.