Online LEGO related resources

Please note these are not officially affiliated with, or endorsed by, LEGO.

Feel free to add more links to this thread, thanks.

Buying and selling
http://www.bricklink.com/ (allows you to filter by sets, parts, instructions, original boxes, catalogues, etc.)
http://www.brickarms.com/ (military themed minifig weapons and accessories)

Guides
http://brickset.com/ (old and new official sets)
http://www.worldbricks.com/ (Instructions and catalogues library)
http://www.peeron.com (Parts database / listing for sets)

MOCs and Adult Fans of LEGO sites (AFOL)
http://www.brickshelf.com (Fan MOCs)
http://rebrickable.com/ (Instructions for alternative builds - includes both official and fan made ones)
http://www.hispabrickmagazine.com/en.../tags/download (Free AFOL LEGO PDF Magazines)

Great links Sam. Use a number of those. Here's a forum site like ozformers but for lego. Not as much activity on there but a handful of regulars seem to post.

http://aussielegofans.forummotion.com/forum

Thanks for the link, good to know there's an active Aussie LEGO forum. :)