Sites for fun problem-solving activities:

Solve a Tangram Puzzle http://standards.nctm.org/document/eexamples/chap4/4.4/index.htm

Play the Fraction Track Game http://standards.nctm.org/document/eexamples/chap5/5.1/#applet

Try a Trivia Quiz

http://www.funtrivia.com/

Can you solve the "Multiplication Mystery?" http://www.hbschool.com/activity/mult/mult.html

Match equivalent fractions with "Fraction Frenzy." http://www.learningplanet.com/sam/ff/index.asp

Did you ever want to build your own dinosaur? http://www.hbschool.com/activity/dino/build.html

What could make learning vocabulary more fun? How about Vocabulary Pinball? http://www.playkidsgames.com/games/pinball/default.htm#

Learn how to play chess

http://www.chessdryad.com/education/magictheater/

Play chess against a computer

http://www.nabiscoworld.com/games/

Try your hand at some "Power Proofreading." http://www.eduplace.com/kids/hme/k_5/proofread/proof.htm

Tell time with Willy the Watchdog http://www.hbschool.com/activity/willy/willy.html

Test your grammar skills with On-line English Grammar Tests http://www.usingenglish.com/quizzes/index.php

Design a roller coaster track that gives your test rider a thrill but not a spill. http://puzzling.caret.cam.ac.uk/game.php?game=roller

Build a roller coaster and ride it

http://virtual.questacon.edu.au/rollercoaster/

Consider starting speed and friction when designing a steel coaster. http://www.sci-quest.org/home/just_for_kids/coaster.phtml

Logical thinking problems and puzzles

http://school.discoveryeducation.com/brainboosters/

Do you know your states?

http://jimspages.com/States.htm