I make most of my money from Adsense, Amazon and eBay but you can post occassional affiliate links in your hubs. I wouldn't recommend posting the same links over and over throughout different hubs though.
Another way I make money is through my own personal sites that I link to sometimes in my hubs and on my HubPages profile.
Write hubs with good content, promote them properly and they'll start showing up in the first couple pages of Google's search results. Most of my traffic comes from search engines and it gives me a steady flow of income.