Shopping square have good prices on flash memory, I recently bought a couple of Kingston 16Gb cards after a recommendation from a photographer mate. Their prices are excellent, freight reasonable and they don't sell dodgy cards.
It's worth noting that the larger the card, the longer it will take to transfer to your PC. Look for a transfer rate of at least 15Mb/s, at that speed a full 2Gb card will take around 15 minutes to transfer to your HDD. If you're after some fast add on storage they also have 1Tb Astone external eSATA/USB drives at just $159