Campag Ultrashift - Chorus, Record, Super Record - lever behind the brake lever moves it up the cassette, button moves it down MULTIPLE sprockets (up to 5 as mentioned).
Campag Powershift - Athena, Centaur, Veloce - lever as above, button only shifts one sprocket per press.
SRAM - lever behind the brake lever only, small press moves it down a gear, press futher in to move up (if i recall correctly about 3 at a time max).
Shimano - as mentioned previously although older Sora (8 speed) had a button that cant be reached form the drops to move down the cassette so not ideal.
I've got/had all 3 systems although not used Powershift (my old Campag 9 speed Mirage has Ultrashift).