I went to high school with two Chilean kids and one year I spent Christmas Eve with their families. I ended up learning some Chilean Spanish expressions. Here are some interesting ones:

¿Cachai? – Do you understand? Get it?
Agarrar p’al hueveo/leseo/chuleteo – make fun of someone
Al tiro – right away, immediately
Año de la pera – many, many years ago
Cabra/o – girl; boy
Cabra/o chica/o – young girl/boy
Chupar – to drink (alcoholic beverages) a lot
Colarse – to crash a party
Copucha – gossip
Cuico/a – snobbish high-class person
Guagua – baby
Guata – belly
Huevón – jerk, idiot
Llorar a moco tendido – to cry one’s eyes out
Lolo – young man
Mijito – Chilean way of addressing someone (it comes from Mi hijito, “my little son”.)
Pajarón – absent-minded
Pisco – a kind of aguardiente
Pololo/a – boyfriend/girlfriend
¡Por la cresta! – Holy cow!
Poto – buttocks

If you have advanced Spanish read this article about Chilean Spanish on La Página del Idioma Español (http://www.elcastellano.org/espachil.html).