Argentina

abombado- stupid
andar con trompa- to be in a bad mood
bacan- someone who is rich or pretends to be
bailanta- nightlucb
boliche- nightclub
bondi- bus (colectivo)
cana- policeman
che- hey
chorro-thief
guita- money
laburo- work
una luca- a thousand pesos
mina- girl
morfar- eat
pibe- guy, dude
piola- cool
pucho- cigarette
quilombo- a mess
tacho- taxi
tarado- stupid

Costa Rica

ahorita- sometime, some day (maybe never)
bicho- a creep, a jerk (lit. insect, slug)
burdo- a bum (lit. an adj., rude)
desayuno tipico- arroz y frijoles
mariposa: a gay
puña: "polite" form of puta, frequently, as in English: s**t
púchitca: variant of puña
pura vida: the good life, used as a very upbeat "ciao"
pulpería: a village 7-11
que rico: super!

Thanks Howard J!

Bolivia

bife- punch
buitre- vomit
buitrear- to vomit
cachar- to catch, to understand
camba- someone from the south of the country
camote- in love
clefa- someone who shows up when they're not invited
colla- someone from the northeast of the country
conchudo- lucky
cuero- good-looking (invariable)
chacharse- to play hooky from work, school
chaki- hangover
chaki moral- strong regret
chapaco/a- someone from Tarija
chapar- to kiss
despute- chaos, mess
gallo- someone from the US
jacho- police agent
k'anka- person from the US
largado- broke (without money)
maldito- awesome, great
pichicata- cocaine
ranfla- promiscuous woman
yeta- bad luck

Central America (gen.)

aviador- a government worker who only shows up on payday

El Salvador

casamiento- rice and beans
chucho- dog
cipote- child/kid
cuche- pig
guaro- trago
pisto- plata
puchica!- more polite expression that the altervative
quilio- militar

Colombia

un bacan- a cool guy
bacano- cool
berraco- Fantastic/astute person
cachaco- person from Bogota
cantaleta- Rambling, sermonizing conversation
chevere- cool
dar lata- to annoy, bother
un gamin- homeless person, bum
gomelo/a- spoiled rich boy/girl
miercoles!- euphemism to avoid saying 'shit'
olla- drug dealing location
un policia acostado- speedbump
un rollo- a mess
un rolo- person from Bogota
que chimba- How cool
qu'ubo parce!? -What's up man!?
sapo- person who gosspis
una zorra- a horse drawn buggy used by poor people in Bogota usually as cheap furniture movers or recyclers

(Thanks Ben, Aiajhz and Erwin)

Mexico

chamaco- small child
chido- cool
mande- what
naco-boorish, uneducated peron
popote- straw
orale- ok
ya mero- almost

Panama

un blanco- a cigarette
chicha- juice
el chino- a corner store
el diablo rojo- bus
una fria- a beer
una pinta- a beer

Paraguay

abatatarse- to lose one's nerve
agati- dragonfly (guarinismo)
bachicha- Italian
banderola- fanlight
batacazo- windfall
bolada- opportune moment
bolilla- topic
cachada- joke
cama- udder (guarinismo)
canaleta- gutter
carpir- to hoe
chiche- small
despachante- customs officer
desprender- undo (button)
guaso- rude
habia- blackbird (guarinismo)
karai- senor ( guarinismo)
lavandina- bleach
merengue- mess
mitai- child (guarinismo)
negociado- shady deal
palenque- tethering post
paseandero- inclined to go out a lot
patotero- hooligan
petizo- short
pituco- snob
pozo- pothole
rebuscarsela- to get by on your wits
retacear- to be sparing with
retar- to tell off
soquete- ankle sock