How do I know if it's any good?

Is the information you are finding correct and valid?
Students need to be able to recognize the difference between a commercial or opinion page and a valid source of source of information. 
Spontaneous Combustion: How To Tell If Your Head's About To Blow Up

Velcro
    

vaprima.org
http://www.ovaprima.org/
Bonsai Kitten
http://www.BonsaiKitten.com/
California's Velcro Crop Under Challenge
http://members.unlimited.net/~kumbach/
velcro.html
Clones-R-Us Homepage
http://www.d-b.net/dti/
Mankato Minn.  Homepage
http://www.lme.mankato.msus.edu
/mankato/mankato.html
True But Little Known Facts 
About Women With AIDS
http://147.129.226.1/library/
research/AIDSFACTS.htm
Feline Reactions to Bearded Men
http://www.improbable.com/
airchives/classical/cat/cat.html
Ladies Against Women (LAW)
http://www.well.com/user/gail/ladies/
Alex Chiu's Eternal Life Device
http://www.alexchiu.com/
Skeptic Tank
http://www.linkline.com/personal/frice/index.htm
The Energy Machine of Joseph Newman
http://home.earthlink.net/~josephnewman/
Worldwide Labs' Melatonin Central
http://www.melatonin.com/
American Smoker's Alliance
http://www.smokers.org/
Halloween
http://www.jeremiahproject.com/halloween.html
National Smokers Alliance
http://www.speakup.org/
(K-) Mart Sucks!
http://www.concentric.net/~rodf/mart.htm
The Useless Pages
http://www.go2net.com/internet/useless/
Fraudulent Site
http://www.mcwhortle.com/

http://www.martinlutherking.org/

http://www.smokers.org/

http://www.martinlutherking.org/

• Some sites have such large files they take a long time to download.
• Some sites require additional software to use (Adobe, Media Player)
  Federal Tax Forms http://www.irs.ustreas.gov/prod/forms_pubs/pubs.html)
  PBS Kids (http://www.pbs.org/kids)
• Some sites are designed poorly and are difficult to read. 
  http://www.worstoftheweb.com/classic/