Feature Set:  

This service, through istock International, does not offer subscriptions but you can purchase credits that start out at 10 credits for $10 and decreases to 625 credits for $500. Generally, you can download a wide variety of 600 X 800 pixel images or flash files for one credit. They also offer one free photo download per week.

The licenses they offer are for one computer and one user.

Their membership is free and you have access to your own private lightbox. You can also login and monitor or add credits. The service lets you know how many times a particular image has been downloaded and will allow you to email an image before you purchase.

Search/Sort Options:  

istockphoto.com offers a color search option as well as by file type, orientation, photographer and size. They offer a one-of-a-kind CopySpace search, which offers a grid of six boxes that can be selected to be open for copy or to contain the image.

Quality:  

For such a low price, their quality is respectable, including some concept imagery and artistic photos.

Selection:  

They offer a good selection of photos, with some vector illustrations, flash files and concept images. They do not offer editorial images per say, but some images are targeted enough that they could be used to convey a specific message. They also offer some isolated images.

Just the price alone is a good reason to investigate this service, but they also offer vibrant concepts and images that carry a voice. This is a popular site, that performs many downloads, however, if you need a managed rights image or commissioned work it may be worth your money to look into some of the more selective collections like those offered by Getty or Jupiter Images.