Geocaching.com was the first major cache listing website and has the vast majority of caches listed on it. It is a for-profit site run by US corporation Groundspeak. This site lists most caches in Australia but can be quite US-centric and somewhat politically correct. Basic access is free and there is fee-based membership for functions such as downloading caches in GPX format and receiving electronic copies of cache pages in a format suitable for PDAs.
For a full history of Geocaching.com, see the History of geocaching.