At this website you will find over 5,000 free stock photos that you can use for just about anything (mind the warning about products being in the pictures because trademark usage can get you sued).
The photos are really easy to navigate. There are an assortment featured on the main page and to the left of them is the navigation menu that lists all the different categories of images you can search through.
The categories are: Animals, Buildings, City, Drinks, Flowers, Food, Gardens, Insects, Interiors, Landscapes, Lights, Macros, Miscellaneous, Objects, Ocean, Panoramas, People, Plants, Space, Travel, and Vehicles.
Each category has subcategories that will drop down when you click on the main category heading; this makes it easier for you to narrow down your search. For example if you were to click landscape the dropdown would provide you different kinds of landscapes to choose from like: fields, forests, lakes, mountains, roads, and sky.
Enjoy browsing the photos!