Believe it or not - Gamecube was the name that was supposed to have been Dreamcast! ;)

Yuji Naka posts a column to Sonic Team's web page every now and then (see previous and below articles), and the latest entry contains an interesting revelation. Apparently, when Sega was deciding upon the name for its new 128-bit console, Sonic Team looked at the shape of the system and suggested "G-Cube." If Sega had taken Sonic Team's advice, we may just have ended up with the Sega G-Cube instead of the Sega Dreamcast. Hmm… perhaps Nintendo would have then opted to release the Nintendo Dreamcast?

Source: IGN DC