I remember in Resident Evil code veronica if you wanted to check you're life you just looked down at the little VMU screen through the controller and it would have a sort of heart beat monitor showing how you're character was doing. Ready to rumble used to have to bars one showing your stamina and the other showing how many punches thrown (I think) However most games just had some sort of moving picture or logo there. Street fighter games usually had the "CAPCOM" logo.
What made the VMU's so cool though was stuff like in Soul calibre, when you completed the main game with certain characters, they would give you a mini game that loaded onto the VMU for you to play. Sonic adventure let you raise your Chao things on them like feed it and pet it etc. You could even connect two VMU's together to trade data (make two chaos meet each other for example).
Man it’s a shame the dreamcast didn’t have a full life, it really was an awesome console.