Here are some great resources to find better images.
This is a fantastic place to find higher quality images for your presentations and image copyrights on this site are governed by Creative Commons licenses.
Pixolu is a semantic image search. After returning your image results, you can select the images that are most relevant and Pixolu will perform another search for similar images.
Viewzi offers 18 different options to view your results that are very visual and easy to explore.
SearchME allows you to flip through the images using an iTunes like browser and you can opt to display textual information for each site.