Here are some interesting links.
General
Lawrence Leung's Choose Your Own Adventure - Setting out to achieve childhood dreams can lead to lots of adventures.
Metal Detector Hire - A real life treasure hunter!
NASA's Astronomy Picture of the Day - The best source of high-resolution pictures of extraterrestrial treasures.
Treasure Hunter: Kirsten Gum - The diverse approach to treasure taken by this show is neat. Particularly cool are the toolkits.
Treasure Hunting Wiki - The Travel Channel's collaborative wiki, a great idea but with a strong US/Canada focus.
Getting Around
Google Maps - Nothing beats this as a starting point for where you are and where you're going.
TripPlanner Sydney - Probably the best (free) way to scale Sydney's public transport system.
TripView - By far the best (non-free) way to get around Sydney. TrainView is the non-iPhone version.
Investigating
WolframAlpha - A useful source of facts, particularly physics and maths - and the best online calculator available.
Physics
AstroPhD Forum - A new online forum aimed at PhD students (but open to all!) to help with astro questions.
AstroPhD Journal Club - Journal club for the AstroPhD forum, for sharing papers and asking questions.
Geocaching
Geocaching.com - Is there any site more authoritative than this one? Probably not.
Garmin Geocaching - A super-awesome guide to making Garmin geocaches available on-the-go.
Geotalk Podcast - A series of podcasts produced in Australia about geocaching and tools for cachers.