Here are some useful websites that I've found:

Reading and Phonics

Starfall -- my kids love this! Jaime learned how to read after a few weeks of lessons.
ReadWriteThink -- this game teaches kids short and long vowel sounds
Story Maker -- write your own Fairytale, Horror or Science Fiction story!
Create Your Scenario! -- direct your own play with these woodland friends
Noun Explorer -- go through the cave by following the nouns
Sorting Words -- sort the words by verb, noun or adjective
Writing Stories -- an interactive lesson on how to write your own story!
Tell a Rex -- Answer funny questions with a yes or no, then get to feed the T-Rex!
Look, Cover, Write, Check -- a spelling game
Cluster Buster -- guess the correct letter cluster in the picture or get hit by an asteroid! 

Civics and History

Find the Hidden Dangers -- Look for the hidden dangers in the neighborhood
Playground Puzzle
Playground rules

Science

National Geographic Kids -- loads of fun information on just about everything!
BBC Science Clips -- interactive clips for kids ages 4-11
Change It! -- what happens if you put items in a freezer or oven? (solid, liquid, gas)
What's the Weather? -- read the thermometer and help dress the bear
Find Earth Materials -- fun interactive game that teaches kids about earth materials in every objects
World Continents Quizzes -- learn the names of the continents and oceans
Thirstin's Water Cycle -- interactive presentation of the water cycle
The Water Family -- build your Water Family and see how you can save water in your home!
Great Plant Escape Case -- learn about the parts of the plants by solving the case!
Magic Watering Can -- find out what kind of plant grows with three easy steps!
Jolly Green Giant -- help the stranded astronauts when you visit the Jolly Giants and learn loads of nutritional facts!
Matching Game -- match the letters to form fruit and vegetable words
Growing Plants -- can you help this plant grow?
Root Race -- help these root crops grow!
Food: A Fact of Life -- find out through these games how food gets on your plate
The Life Cycle of Plants -- learn about seed dispersal, parts of a flower and more!
Watch It Grow -- plant your seeds and learn all about the parts of a plant
Design a Garden -- make your own garden
Where Is Wood? -- tag each item that came from a tree
Coral Reef Creatures -- identify the creatures in a coral reef
Great Barrier Reef -- learn about the endagered species in the great barrier reef
Deep Sea Creatures -- find out the weirdest creatures living at the bottom of the ocean!
Earth, Moon and Sun -- An Interactive Learning Experience!
Phases of the Moon -- learn why the moon changes shape each night
Moon Watch Flip Book -- make your own book about the phases of the moon
What Shape Is The Moon? -- Join the campfire and learn all about the moon
Intersteller Trip Planner -- find out how long it will take you to travel through space
NASA Kids' Club -- be an astronaut!
Tonight's Sky -- learn about the constellations on tonight's sky
The Space Place -- all about stars, galaxies and black holes
Astro Adventure -- wanna go on a space trip?
Day and Night -- an interactive explanation of the earth's rotation, seasons, night and day
Galaxies Galore, Games and More
Seasons Games -- categorized according to seasons
The Four Seasons -- drag and click which season is on the picture
Can You Place Me? -- complete the seasonal picture
Why Is Spring In The Air? -- find out how the movement of the earth affects our seasons
Animal Games for Kids -- get to know all about animals through these games!
Body Parts -- match the word to the correct body part
Your Amazing Senses -- connect the body parts that sense the correct things 

Math

ICT Games (Numeracy) -- fun games that help reinforce mathematical concepts
Connect the Dots by 5's and 10's -- find out the hidden picture
Wealth of Links -- lots of links to fun learning sites
CoolMath4Kids.com -- practice your math skills the fun way
KidsNumbers.com -- more math exercises
Puny Pet Shoppe -- fill up the pet shoppe by adding the numbers
Wade's Workout -- get Wade into shape by adding the numbers
Ants Go Marching -- add the numbers before the ants eat your food!
Callum's Addition Pyramid -- Get a 1000 pyramid points to open the mummy's tomb!
Bugabaloo Shoes -- find out how many shoes the bug needs by counting his feet
Math Popper -- pop the the balloons by adding the numbers before the time runs out!
Pipe Subtraction -- repair the slide by cutting the pipe to the right size
Busy Bees -- find out how many bees went inside the hive
Sub Harvest -- how many apples will be left on the tree?
Snapdragon-Telling Time -- Set the clock to the right time
Telling Time -- click the correct time on the clock
Lil Fingers Telling Time -- fix the hands of the clock to the right time
Fractions -- learn what fractions are and test your knowledge
Melvin's Make a Match -- help Melvin match the correct fraction bottles
Fractions Made Easy -- learn all about fractions!
Matching Fractions -- match the number to the shape
Partition -- Count the blocks and guess the correct number (Math U See compatible)
Great Day for Number Line - Add/Subtract using a number line
Penny Prizes -- guess which number is greater/lesser and earn a gumball!
Identify 11-30 -- Math U See compatible
Counting Objects -- Uses a graph
Numbers -- contain Math Model tutorials perfect for Math U See
Stacker -- stack the boxes in order
Count on Me -- an interactive lesson and games for addition and subtraction
Ordinal Numbers -- an interactive lesson and game for ordinal numbers
Caroll diagrams -- lesson and game for grouping
Times It! -- an interactive lesson for multiplication
Counting with Teddy -- addition using number line
Save the Whale -- Fix the Number Bond pipes up to 10
5 and a bit Ogre Hit! -- hit the ogre by adding numbers using bonds of 5 
Flight for Fuel -- earn space fuel by adding the correct numbers needed for the fuel box
Catapult Count On -- destroy the castle by throwing stones using the number line
Mucky Monsters -- who has more/less bugs on their hands?
Rabbit -- feed rabbit with the carrot that has greater/less than the number given
Frog -- help frog by adding the numbers using the number pods
Lifeguard -- save the drowning person by using 10's and 1's
Shark Numbers -- guess the number blocks correctly before the shark eats your boat! (Math U See)
Arrow Cards -- create a number using number cards by 100's, 10's and 1's
Dino Place Value -- help the dinosaur by guessing the number using place values of 10's and 1's
Partition -- Count the blocks by 10's and 1's to guess the correct number (Math U See)

Filipino

Digital Dialects -- learn Tagalog with these interactive games

Bible Study

Beth's Bible Study -- has great interactive lessons and study guides according to topics

Music and Arts

Kaboose Music Games -- learn all about music
CraftBits -- simple craft ideas
Circus Simon -- stack up the circus performers by following the musical pattern
Living Colour -- learn about colours!
ScrapBlog -- an online scrapbook site

Home School Resources

Homeschool Rewards and Benefits -- great site for the homeschool newbie (like me!)
Pete's PowerPoint Station -- the mother of all online educational materials!
Fun4theBrain.com -- educational games by subject
KOL Homework Help Jr. -- great kid-friendly interactive activities
PrimaryGames.com -- The fun place to learn!
Kaboose FunSchool -- fun learning activities and games
NGfL Cymru -- Welsh teaching website with interactive lessons and games