Buy cheap .info domains and put up original content sites. Build links and sell the sites. That will involve work but you could make money.
spend at least 1 week reading everything, blogs, forums etc.. never buy an ebook work 18 hours a day work hard dont take shortcuts or be lazy
A fast way to double or even tripple your money would be joining HYIP or autosurf sites. It's very risky but rewarding.
Getjimmy i think there is some confusion at your end OP want to earn more profit from $100 he is already having with him if i am not mistaken. I suggest OP to buy a good .com domain and start a blog with niche in which he/she has good knowledge and try to promote it through several directories submissions etc. in first stage. DON.