I will preface this hub with the words I am a secondary Science and Mathematics teacher and therefore many of the sites that I recommend will be from these areas... I am also an Australian teacher and I appologise for the antipodian nature of many of the sites I use:

Science

http://www1.curriculum.edu.au/science/ This is a great start for Science teachers who are looking for ideas

Mathematics

looking for Authentic and rich maths tasks look no further than http://jonathan.mueller.faculty.noctrl.edu/toolbox/examples/examples_tasks_math.htm

http://www.blackdouglas.com.au/project/taskcent.htm is also a good place to look for help with tasks

http://www.nku.edu/~mathed/mori.html for quizes and questions

http://www.mathletics.com.au/ this is a site that you need to pay for but they have great resources for schools and for individual students

http://www.eaa.unsw.edu.au/prepare/practice_questions This is site for the University of NSW compettion, some great practice questions 

Other

http://www.det.wa.edu.au/education/cmis/eval/ This is a Western Australian Site that is run by the Department of Education, they troll the net for good sites a great place to start looking for ideas and resources

http://www.enchantedlearning.com/Home.html some of the information on this site you do need to pay for but there is a lot of free stuff here. 

Cybersafety http://www.thatsnotcool.com/ think that you are being textually harrassed, get some advice here! Another good information site is http://www.netalert.gov.au/