wow im amazed no one has this one, its pretty barebones but its free, from ejunkie who also has some sort of ecart srvice,

fatfree isnt actually a whole system, you just paste the code and it looks really neat when you check out, basically it just transfers your checkout to paypal or google or 2checkout or something like that, anyway i recommend it for anyone whos not to familiar with bigger systems mainly bc you dont have to "skin" it, rather you plug it in, to your good old html site