WoN-Boots: Unlock sparkly boots (decent stats, mostly fun for the on-screen effects)
Holiday-Man: Unlock Holiday Man Christmas quest
Best-VA: Unlock April Fools "High-Quality" Voice Acting, you can also disable voice by re inputting the code again.
Caramelldansen: lea does the dance from this video https://www.youtube.com/watch?v=zvq9r6R6QAY
Speedlines: Enables in-game speedlines
Regular-Trees: Makes some trees more regular

I do not know of other codes and if I did know, Im not sure I would be allowed to post them
"Devs have said these two codes are fair game now, so don't worry about spreading these anymore in discussion forums and let everyone know."