As ever, this really, really depends on what kinds of things you scrapbook. Do you scrapbook about kids, pets, hobbies, cooking, travel? Do you want to do page titles in a lot of different fonts? Do you make cards? Do you prefer simple or realistic or cartoonish designs?
The cartridges Ruby suggests would have to be found on eBay or another third-party seller, unfortunately, as otherwise they're both only available bundled with new machines.