the number 1 upgrade for most people I knew was the 512Meg expansion
I must say i doubt that just a little. Even an 80 MB harddrive was big bucks back then, let alone a 512 MB ram expansion... :-P
I wasn't even aware a humble A500 could adress such a large area of ram. ;-)
Or do you mean 512 KB? Those were slightly more common compared to 512 MB... Oh well, KB, MB: who minds a factor of 1000 more or less.. :-)