For the most part, I have been able to get many great quality images on the many free stock photo websites. Here are a few of the places I use as resources for great free and low-cost images for your marketing.
I recently found that Etsy is a great source for quality low-cost vectors. When I design a logo, I draw it out by hand then turn it into a vector in Illustrator. Some of the parts are hand drawn with Illustrator by me, but others it is just so much easier to use something pre-made, especially the more complex illustrations. I have found high-quality illustrations you can download instantly for as low as $5 or $10 a pop, as opposed to $30 or $50 from the most popular stock image websites. Etsy has really grown in that it now offers downloadable files such as images and vectors you can use for your branding and marketing.