yup I used to have game genies for all of my cartridge based system... those things were awesome.
unfortunately most gamers today consider the PS1 to be a "classic" console which IMO is ridiculous... they did have Game Genie but it was little more than a save game loader
I'd love to see a similar system for modern consoles... at the very least something that could do save states in the memory would be tremendous.
action replay had some cheat benefits, i had it for dreamcast and GBA, i think there was one for PS2 that would let you cheat too
the trouble is for the CD/DVD-based consoles you need to set up the GG/AR device with a boot cd (the dreamcast AR was a boot CD with a large memcard) but consoles now dont want to let you use any kind of boot disc because of piracy