This list is by no means comprehensive, but I have tried most of these and enjoyed them very much! I may keep adding to this so we can have a database of tried and true crafts! We'll see . . .
Lucky Ladybird's Plastic Bag Coil Basket This is best suited to the ambitious since it takes time and tenacity to hold down the coils as you bind them. Maybe if you aren't feeling so bold, you could use the same technique to make coasters. I just like the idea of using plastic bags for something since they aren't biodegradable. This was my first stab at basketry, and I found it fun. If you know how to knit or crochet, Ladybird has a tutorial on making yarn out of plastic bags, as well as some other fun projects.
Creative Jewish Mom's Polyhedrons- Those who know me see them displayed hanging from the ceiling in my classroom! They are very addictive! Also time consuming, but again, what a nifty result! If you make a small one, card stock works well and makes a fine ornament. Don't use wrapping paper, it ripples and slides off of cardboard because of its waxiness. Glitter glue finishes these off nicely, if you like a bit a sparkle. While we're at it, CJM has TONS of other fun crafts on her site. I am hoping to try the fused plastic bag coasters and the felt roses sometime soon, too.
Fluffyland's Starburst Wrapper Bracelet- I remember making these as a kid, and the bonus is you get to eat candy in order to make this! Other wrappers are suitable, too, but Starburst is a colorful and easy to acquire. Not too hard compared to the others I've included.
Folding Trees' Kusudama Flower/Ball- I am currently adoring these and making a funky flower arrangement of my own. The Kusudama ball is very impressive, but it takes 60 pieces of paper and a lot of time to make. It's surprisingly heavy, too. Not a confusing craft, but you must be dedicated to finish one! I have one seriously helpful hint for those that attempt this one: Use hairpins to pinch the petals and flowers together while the glue is setting. This will save you a lot of waiting! There are other great paper craft tutorials on this site. If you want something cute and easy, try their paper star instead.