hahhaahaha "Ay caramba" it's like sayin: oh my god!! (kind of) you could also say: oh dios mio!! ay dios! all the 3 of them express surprise. there are many more expressions but they are kind of rude XD hope it was of any help n_n Adios!

In Peru there are many interjections: ¡Ah caray! ¡Caramba! ¡Cielos! ¡Rayos!, etc. Personally I say: ¿En serio? ¡No lo puedo creer! ¿Qué?

I found this about the etymology of it

http://www.etymonline.com/index.php?term=caramba