Apple III (1981): Hardware was unreliable, and the Apple lost the business market to the IBM PC, launched the same year
Lisa (1983): The first commercially produced computer with a graphical user interface, costing $9,995 when launched
NeXT Computer (1989): In many ways ahead of its time, it was also too expensive to catch on with mainstream users
Puck Mouse (1998): Users couldn't tell which way it was oriented by feel, and it tended to disappear in the cup of the hand
The Cube (2000): High price was the main deterrent. Also, the computer didn't really offer any functional benefits over other Macs.
iTunes phone (2005): Unexciting as a phone, it fell far short of the iPod as a music player
Apple TV (2007): Expensive at $249, it was complicated to set up and use.