Clifford The Firehouse Dog (Paperback), by Norman Bridwell. Our first Clifford book, this one was grabbed on the way out of the library, because I wanted something with fire engines in it (a recent favorite). Haven't made it through it yet (only 14 months), but he enjoys the first page or two and then moves on.
"I asked the firefighters if Clifford could help them. They thought he was the right color for the job."
Bookworm's interest at 14 months: Making a siren noise when he sees the fire engine.