I'd say the Walkman gets that honor, if not some other product.

The iPod was popular because it was the first practical MP3 player. Take a look at the competition:

http://www.examiner.com/list/five-portable-mp3-players-that-...

You've got reasonably sized devices that could hold a few dozen megabytes, or impractical tanks that had real capacity. The iPod was the first to do both. It also had a user experience that was quite painless.