Are there standard words to represent sounds in Esperanto, or can they be made up on the spot? If the former is true what are some common Onomatopoeia.

A few that come to mind immediately: klaki = to click, pafi = to fire a gun (paf!), susuri (=to rustle).

I just yesterday received J.F. Conroy's "Ee-Eo/Eo-En Dictionary and Phrasebook," and I'll share with you its section on onomatopoeia ("sounds and feelings," as they put it):

aha! - ah ha!
aj! - ouch
ba! - disbelief (bah!)
bam - sound of a large bell
baŭ! - woof!
bis! - encore
brave! - bravo!
bum! - boom! (cannon, drum)
ĉit! - shhh!
ek! - hurry up!
fi! - how depraved!
for! - get away from here!
fu! - whew! (fatigue)
glu-glu - sound of water
haltu! - stop!
he! - yo!
helpon! - help!
hu! - yuck!
hum - hmmm...
hura! - Hurray!
Jen! - Well, there you go!
ĵĵĵĵ - swish (sound of clothing)
klak,klak - clap clap (applause)
kokeriko - cockle-doodle-doo
kribel, krabel, bum! - Sounds of someone taking steps, then falling
miaŭ - meow (cat)
plaŭ - splash
ta-ta-ta - yaddah-yaddah-yaddah
trateratra - ta-DAH
ve - oy
vivu... - long live...
zum - buzz (as of bees)

That's what they say, at least.

Anything for WOW! ???

Vaŭ! maybe?

I think "wow" is "ho"

I would like to know what is it for cow? :)

I would like to know what is it for cow? :)

muŭ, perhaps :-)

To add to the list, there's "ho ruk", which is used when one or more persons are lifting something heavy. (hooooo ruk!)

I don't know of a list anywhere that has this; anyone know a good place we can start accumulating such phrases? There's the MEK, a wiki that anyone can edit, but it's not very big yet. Perhaps a wikipedia entry would be proper. And the Esperanto Wikipedia as well. I'd like to see the onomatopoeias used by esperantists from other countries, too. Ĉu ne?

I think "wow" is "ho"

Ha and ŭaŭ are both valid here.

I would like to know what is it for cow? :)

It's mu.

I don't know of a list anywhere that has this; anyone know a good place we can start accumulating such phrases?

I've been collecting some onomatopoeia and interjections, working from lists I've been able to find, at this page in Vortoj wiki (It shares a page with curse words, perhaps it should be split...) The list is quite long!

I just yesterday received J.F. Conroy's "Ee-Eo/Eo-En Dictionary and Phrasebook,"

I've got that one, "kribel, krabel, bum" is just amazing, does anyone actually use it?

Everything seems quite clear ("kribel, krabel, bum" made me laugh though ), but what does 'yaddah-yaddah-yaddah' mean?