Blue's Clues

Blues Clues is quite popular with toddlers and preschoolers in the U.S. The show has a "host", more like a main character (originally Steve Burns, who was very good, now "Joe" Donovan Bratton) who introduces a scenario and leads the viewers through a sort of "scavenger hunt". The hunt is guided by hints from talking things in the house (e.g. slippery soap, tickety tock and the salt, pepper paprika family), with the targets of the search marked by the girl puppy, "Blue", using paw prints (hence Blue's Clues).

The secret to the show in my opinion is that it has a nice formula, and more importantly the host treats the audience in an engaging manner and are NOT condescending (I think a lot of shows talk down to kids and they can pick up on it). Steve retired from the show (they told the audience he was "Going to College") and his brother Joe was going to take over. Steve was especially good at dealing with the audience (many adults secretly enjoy the show, Steve is pretty good), but his recent replacement by Joe seems to have gone well and I think Joe may do well (although I still like Steve a bit better, Steve had more practice).