Build a Niche Store - This is a simple store development platform which enables you to create content based sites that generate income through the eBay affiliate programs. Pretty darn simple and increasingly popular.
Adbrite - Sell space on your site for text ads. This would work like the DLM Marketplace you see on the right of my pages although I chose to manage it myself.
Amazon Affiliate Program - Easily create a store or shopping section on your site instead of sending your visitors to Amazon. Amazon handles the shopping cart and fulfillment.
Amazon Seller - Sell your stuff on Amazon
Associated Content - If you write a story, how-to, rant, how-to cut grass, etc., you can submit it to them and they will pay you $3-$20 per article if they like it.
Yahoo! Merchant Solutions - This is a pretty simple and cheap way to create an online store.
Azoogleads - Another ad program. They do have some decent companies lined up as advertisers. You provide space, they'll provide an ad.
BidVertiser - PPC (pay per click) program with a low $10 payout amount.
Blog - Start a blog and consistently write excellent content. With good ad placement, you may make some money. I detail my process here: Simply Said, How to Blog.
Cafepress - You provide a design, they'll toss it on a T-Shirt, Hat, etc. No upfront costs. Get a free online shop and promote your products on your website.
Chitika - Their eMiniMalls service has shown great results for many Bloggers and site owners. You choose a keyword and they show relevant products on your site using a pretty unique interface.
Clickbank - Quickly becoming my favorite affiliate program. They have thousands of things for you to advertise on your site.
ClicknWork - Get paid $5-$150 per hour for basically doing freelance work on a per-assignment basis. You have to pass a pretty tough test to get in.
Clicksor - These are the guys that generate contextual ads on sites that show up when you hover over a double-underlined word.
Commission Junction - If you have a site, you can join Commission Junction. Once enrolled for free, you can choose companies whose ads are pertinent to your site. Companies have the ultimate say on working with you. There are easily over 1,000 companies to choose from here.
CreamAid - For blogs only, advertisers provide you with a topic and you write about it on your site. To do this, you have to install a flash widget into your blog post. The more people you bring into the conversation through the widget, the more you get paid. It's difficult to explain.
eefoof - Think of it as YouTube + Flickr + Music. You add original content and they pay you based on the visitors you attract.
Ether - If you are an expert on something, Ether provides a way for people to pay you to talk about it in a one-on-one setting. If you want to charge $250/hr, that's fine. You have to do all the advertising so you should have a blog or site already established.