Some blogs are focused on getting paid to provide links to news articles, company stores, or other third party websites. The most financially successful of these range from the Drudge, a blog composed almost entirely of conservative-leaning news links, to Smashing Magazine, a site that provides advice and product reviews to help software developers.
If your niche doesn’t allow you to promote or build premium products (anything over around $100 per unit) then think about getting a solid mix of offerings and building it up over time. I remember Darren Rowse saying that initially Amazon Associates was a really small source of income but over the years it has really started to add up. Think eBooks, affiliates, consulting, books, etc. and you’re starting to build an income stream.
Adsense is a contextual advertising network that places partner (business) ads on your website. It’s easy to set up—all you have to do is copy and paste some code given to you from Google in the places you'd like the ads to appear on your website. Google will then show ads from advertisers that are a match to the content on your website so that ideally your website visitors see relevant ads.