so, if you're talking video, MPEG 1 and 2 (.mpg, .mpeg) were used a bunch and got displaced by MPEG 4 (.mp4, .m4v)

if you're talking audio, MPEG-1 layer 1 (.mp1)... wasn't ever used much but existed, layer 2 (.mp2) found quite a bit of use
but MP3s were smaller, and naturally beat out both formats since the tradeoffs were encoding/decoding speed (mp1 is easier than mp2, which is easier than mp3) while hardware got faster