1. Make your own I Spy Books. Choose a theme like colors, a holiday, or beginning letter sounds. Start gathering objects from around the house that fit your theme (or better yet, have the kids do it.) Take and print your pictures, write your clues, and bind them together for your own I Spy book! (There's a great tutorial over at Rookie Moms.)
If your children are younger, you could do an I Spy collage (aka junk collage). Gather odds and ends from around the house (cereal, dried pasta, magazine pictures, foam shapes and letters, google eyes...) and have your preschooler glue everything onto a piece of paper. Then they get to quiz you and see if you can find things.
4. My sister made these I Spy bags for the kids. There's a laminated picture attached of all the things they can find in the bag (including the letters in their names). There's a tutorial for similar ones at Skip to My Lou.
If you're like me and and your sewing skills are non-existent, I saw a great idea for filling plastic zip-lock bags with hair gel at Teach Preschool. Add some little toys and a laminated picture, and you've got a No-Sew I Spy bag (though it's probably not as travel friendly as the sewn version!)
How do you I Spy at your house?