If you asking what I use, mainly my own photos, correctly attributed images, or images from free stock photo websites.
For you, I'd recommend the same things. Get yourself a camera with a slightly better resolution than a potato, and snap away :) You'll often find that these pictures are the nicest to feature on your articles.
Alternatively, websites like deviant art host an array of wonderful pieces, and the artists are readily available to email and request use. As long as you ask permission and attribute them correctly they will normally be happy of the appreciation.
Free stock photos are very easy to find, if you go to google and type "free stock photos" you'll get a huge list of websites. Browse through them and search for what you need. The downside to this is that often you'll struggle to find photos that compete against the quality and artistic prowess featured on others articles.
I really hope this helps answer your question.