i know of a few...
PCCG is good!
Umart tries to price match... the prices listed on their site arent the cheapest but they do price match if they can...
www.umart.com.au
megaware is cheap and online but not sure if they pricematch... (think they are a distributer)
www.megaware.com.au
MSY is cheap! but not sure if they do online
msy.com.au (no www.)
Centrecom is online EDIT : (they pricematch as well)
www.centrecom.com.au
A Moding specialty store is performance pc's and they are in the US i think and do deliver to Aus...
but only deal with cases and watercooling and such... NO components! though!
www.performance-pcs.com
also try these price comparing websites...
www.shopbot.com.au <----- (think this one is better)
www.staticice.com.au
hope this helps.
P.S. if anyone knows of others I too would be interested in knowing...