it'd really depend on my needs. do i already have a spare monitor, keyboard and mouse laying around? if so, i'd get a mac mini. do i need portability? maybe a used powerbook or possibly even a macbook might be right. it depends on your individual needs. if i had only $600 to blow on a mac, i'd try to fetch a used 1.83 ghz macbook. it might take a bit of time to find, but that's the model i'd go for.