I've explored lots of ways to try and make money on-line. Unless you have strong technical skills it takes lots of time and effort to make very little. Some options are:

Ebay - You can buy things from boot sales (collectables), one day discount sites, alibaba ect and resell. Lots of competition and low margins, very time consuming.

Blogging - If enough people read what you write you can put adds on your sites or sell space if it's subject specific.

Affiliate Marketing - loads of ways to go about this, best of to torrent some ebooks, but be careful with buying adwords as you can lose a lot money as well.

Sell your skills/expertise - elance.com, fiverr.com, ect

Poker - If your fairly good and disciplined you can make money playing low tables as their is a lot of idiots out there (I only play large tournament's now but have made about £1400 profit in the last year).

Site Flipping - buy sites from flippa.com, make them better, get more traffic and resell them for more.

Domain trading - would avoid this, is difficult and you will probably just end up losing money like I did.

Sure there's plenty more but this might at least give you some direction. But a bit like PU theirs no magic bullets, whatever you try will take you a long time and a lot of work.