Updated 5/10/08 My list of expressive sounds:

phonesthemes
Sound symbolism, also known as iconism
Imitative sound symbolism is the use of onomatopoeia.
sound symbolism is ubiquitous in product names and slogans
A minimal sign is a linguistic sign that does not contain smaller elements
Phonesthetic sound symbolism, also known as conventional sound symbolism or phonetic symbolism,
is the use of sound symbolic elements called phonesthemes.
A phonestheme is a sound, sound cluster, or sound type that is directly associated with a meaning.
(definitions from: http://www.geocities.com/SoHo/Studios/9783/phonpap1.html#manifestations )

ack
aaacck
ah
aha
ah ha ha
ah-hah
ahem
ahh
argh
Ahrrrr
aw
aww

boink
boo
boo-hoo

duh

eh
EEEEEE-AAWWWW EEEE-AWWW
ewe
ewee
Eeweeee
ewey
ewie

fie
frak

ha
haha
hahhh
Hallelujah
hee
hey
hiss
hmmm
hooray
hoot
hrmm
huh
Huh-uh
huzzah

icky

kaBLAAAAAAMO
kerPLOP

ladada
lahdedah
Lalalala

miaow
Mm-hmm
Mmm
mmmm
mmmmm
Mm-m-hmmm

oh
Oh-ee-yoh
Oh-ee-yeah
oo
ooh
ooh-baby
ooh-goddd
ooh-la-la
ooh-ooh
Ooh-ooh-ooh-ooh
Ooh-wee
Ooh-whee
oops
ooooo-ee
ou
ouch
ouchahhh
ough
oui
oui-ee
Ow

owie
oww
owww
owwww

pant
pant-pant
pffft

sigh
smoosh

teehee

uh
uh-huh
uh-hmm
Um-mmm
Umm-umm
umph

wah
Wheeeeeeeeeee
whew
whizz
whoa
whoosh
woo
woo-ee
Woo-ooh
whoop
wow
wowowowowowow

yawl
yea
yeah
yo
yowl
yowza
Yyyyyyyyyyyyyyyessss
yuck
yuckie
yum
yum yum

zoit