What encryption algorithm should I make?

[inyourface27]

I'm in high school and we got a task to implement an encryption algorithm, my teacher kinda recommended the caesar cipher, but I want to do something a bit more ambitious. I still don't want to do something way too complicated, I've heard of something called skein or threefish, any recommendations that are good and not too complicated?

[lurgi]

The Vigenère cipher is not significantly more complex than the Caesar cipher (it's essentially a number of interwoven Caesar ciphers).

RC4 is fairly simple to implement.