How about a treasure hunt (during the warmer months, write clues that lead your kids to certain artifacts, e.g. and oak tree if you're in the park, or a dandelion or buttercup in the garden, that has another clue, and so on until they have collected so many clues, I usually do 15. the first one to get all the clues wins a prize, e.g. a candy bar or they get to choose the movie next time you go).
Collect a box of scrap paper, card, toilet roll middles, candy wrappers, glitter, glue and material. during the colder weather get the kids to design and make their own costumes/masks and then spend time together writing a play that they can perform for the rest of the family. (we used to do this every year around christmas time when I was small)

Library story time and summer reading programs are fun. Last year my 2DD got coupons for free ice cream, tater tots, french fries, small toys and bookmarks just for reading (which they would have done anyway). Pack a picnic lunch for the park, while your there play bubbles, sidewalk chalk, shovels and pails and kites. Set up a tent in the backyard. Use recycled materials for art. Lots of great ideas on the web and I love the magazine Family Fun. Cooking is fun for the kids. Make deviled eggs, banana boats, pretzels, cookies, no bake cookies, slushies, smoothies, fruit salad or kabobs, jello, spaghetti,etc. Swimming at the pool or if it's too far to drive (or gas is still high) use a wading pool or sprinkler. Eat popsicles you make together. Play tag, blindmans bluff, hopscotch, foursquare, catch, or hit a beachball to one another. Turn off the t.v. and videogames and computer and spend time together as a family. Make memories. One last idea my girls love is called "girlie night". When my husband has to work late or is away we get dressed in our p.j.'s, paint each others nails, give each other back rubs and put on a facial. Then we eat pizza and watch girlie movies. A lot of great memories for when they are older and would rather hang out with their friends than spend time with me.

Great Ideas!

Our family favorites are;

Camping
Beach
Biking
Going to the Park and having a Picnic
Swimming at our local Pool
Scavenger Hunts

We tye dye white t-shirts, that well, lets face it are not that white anymore. We all get the color we want and use rubber bands and marbles to create neat effects. It is a fun activity and the t-shirts turn out so cool. Then our worn out, not so white shirts are new again. And we made them!!!!

There are a lot of bookstores that do children's storytime during the day and at night. Pottery Barn kids also has a storytime.

In the spring and summer we like to go to the Botanical Gardens. We play and then have a picnic.

Family game night
play at the park and on the way home get a half gallon of ice cream
ride bikes
walk the dog
go to the school nearby and play basketball
pop some popcorn and watch a movie we already own
go to church activities

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Me and my 4 year old daughter paint everyday. She uses crayola water paints and I use Acrylic paints. Her paints are $6.99 for a set of 8-2oz bottles at Walmart. They wash out with regular soap and water from furniture, clothes and carpet.

We also use Viva paper towels. We rinse them out with soap and water, lay them out to dry and reuse them about 10x or until they fall apart. We paint on paper, newspaper after priming with gesso, junk mail, cardboard, or anything flat.

Michelle S

in our town there is a 1.00 movie theater and on certain days during the week they .50 cent days for groups of 3 or more.