A lot of people start to aware that a site must always come with some graphics but don’t over graphics on your site, that will make your site looks very complicated.
Where can we get the graphics? Below are some of my suggestions:
1) Go to search engine like Google.com, look for “free + your topic” + picture”, get something that you like, edit the picture using gimp (you can download from gimp.org), something that very similar to Photoshop and put it into your site.
2) Other than that, images.google.com will be your second choices.
3) You can hire someone to design for you, which will cost your about USD2 to USD5 per picture if you have the budget.
From the statistics, a site full with picture will intentionally have a good conversion rate if you compare with those without graphic. Just put some picture where it will make your site looks professional too. 🙂