That's a question frequently asked as you start to design a website. A site I just finished creating was particularly fun -- because it was for a therapist -- and my undergraduate work was psychology. We both wanted a fresh clean style that is -- at present -- my favorite. We wanted it to feel "accessible", friendly, while accenting her professional accomplishments. We wanted it to have a warm look, suggesting that through her therapy clients could gain a positive outlook and achieve positive growth.
Susan -- the therapist from Durham -- and I had a great time looking over different stock images to find one with just the right feel to use as a banner. Not too feminine, not too weird, not too sappy or strange. So we chose an image of wheat in a field at sunrise. Suggesting, "it's a new day" and the light is lovely.
I also tried something new on this site and took part of the banner to make a vertical image that moves down the side of each page clicked on from the welcome page.
By the way, Susan has amazing background as a therapist. She has published a lot, presented a lot, and is versed in many different types of therapy. And she is also a painter!
Check out the details at http://www.susanheadphd.com/