Excellent question. I have found in the past that's one of the best things I could invest I was a copy of the Funclips coupon book.
The Toronto edition cost me only $25 and included the tax. It has in it coupons for free passes to Reptilia (what kid doesn't love huge snakes?), 2-for-1 laps at the Innisfil Indy Go-Karts, 2-for-1 laser tag, rock climbing and go carts at the NASCAR speed Park in Vaughan, The Wave Pool in Richmond Hill (perfect for and a cooling off on hot summer days). If your kids are really into adventure you can try out the Wasaga Beach Paintball Adventure at 50% off.
Even if you don't leave the house there's even a free movie rental coupon for video flicks. There's plenty of restaurant coupons as well like a free kiddie meal at Lick's Homeburger & Ice Cream. There's plenty of restaurant coupons there if you want to have a date night with your wife as well at some nice places like Mighty Ducks, Fionn MacCools and Fox and fiddle. I got about $200 worth of value out of my coupon book so it was well worth it for me. you can buy your copy of <a href="http://www.funclips.ca">Funclips coupon book</a> online so you don't have to leave the house with your kids to buy it.