Feature Set:  

This stock photography site offers royalty free photo objects with the simplicity of vector art and can easily be placed into any background. Their subscription costs less than $100 per month and allows up to 250 downloads per day. They offer multiple user licenses as well.

They do not offer full photographs but only isolated images that are pre-masked. They offer a variety of resolutions and sizes including a 'super' at 2339 X 3300 pixels for $199.95/ea.

Search/Sort Options:  

This site offers an excellent color search option. The search box has a color wheel where you can select a specific color or enter an exact color number. You can also search by keyword, category or date added.

Quality:  

The object image quality is good, but the human images do not have the best clarity. This site does not offer artistic type images but only objects and isolated images.

Selection:  

This service only offers one type of product. Currently they offer around 100,000 images.

If you need isolated images, especially objects and want to save time by purchasing pre-masked images then this is a good place to start.