Have learned to do these by heart so far:

1. steamboat (pretty easy)
2. boat (easy)
3. catamaran (took me some time to figure it out, but is not too hard either)
4. crane (standard model - looks awesome and is easy)
5. swan (easy)
6. frog (easy, too)
7. crab (probably the easiest model on the list)
8. iris flower (takes some time to do these, but is not very difficult)
9. dinosaur (one of the more difficult models)
10. rabbit (looks really good and is not too complex)
11. seal (doesn't look that good in my opinion, but is okay and not too difficult)
12. butterfly (tried a few instructions for these with only one good-looking result so far, which is not too easy, but is surely possible to do with some experience)

If anyone wants the instruction pdf's, just send me your E-Mail-adress and I'll send them to you ;) (less)

Have learned to do these by heart so far:

1. steamboat (pretty easy)
2. boat (easy)
3. catama (...more)