When we moved into this condo, the owners left two I Spy books in the bathroom.
How do you need a book or a DS cart to play I Spy? I thought the main (possibly only) plus point of it was because you could play it anywhere when you've got nothing else to do.
Anyway:
UK: Where's Wally
US: Where's Waldo
France: Where's Charlie
Germany: Where's Walter
Denmark: Where's Holger
Norway: Where's Willy
Israel: Where's Effy
So now you know.