Our eyes and brains are trained to pay attention to human faces.  We are drawn to them, we like to look at them, and we will notice them first before any other image or object we see.  

Since you help people and build trust with people and make people's lives better...images of people are great to have on your website and you can use them to draw your guest's eye to an area of your page that you'd like them to focus on.  

So what's better than people?  Happy people (because that's what you do, make people happy!)  I found some great images of happy people for you in the Creative Commons database.  You can use them for free, just make sure to give credit to the artist.