Affiliate marketing is an excellent second income stream. There's no such thing as a truly passive income source, but this comes close. You will have to maintain your website and answer the occasional support question, but mostly, affiliate links aren't something you have to think too much about. You can, in fact, get several of them and typically manage them quite well.

Multiple payment methods is another way to improve the monetizing of your site. Not everyone who visits your site has PayPal. Not everyone that visits your site has a credit card. By getting an account both with PayPal and a credit card service like Authorize.net, you can dramatically increase your income, while minimizing potential penalties with PayPal.

Multiple traffic streams is an often overlooked aspect of making money. The short version of how this works is: The more places your link is seen, the more ways they can come to your page. The more ways traffic can come to your page, the more traffic you get. It's really that simple.

Of course, then you have multiple products. Again, the World Wide Web is called a web for a reason. The best way to increase your profits is not to have the cheapest or most expensive product around. It's having the most products, the most ways to get to your products, and the most ways to pay for your products. You are a spider, of sorts; make your own web and draw the buyers in.