I have used <a href="http://www.fotolia.com/" rel="nofollow">http://www.fotolia.com/</a> and find them to be the cheapest stock photo websites out there.<p><a href="http://www.istockphoto.com/" rel="nofollow">http://www.istockphoto.com/</a> has a much larger collection, but they are a lot costlier.
Not really like most stock photo sites, but it bears a mention:
<a href="http://unsplash.com/" rel="nofollow">http://unsplash.com/</a><p>Awesome quality, free, etc
By far it's <a href="http://morguefile.com" rel="nofollow">http://morguefile.com</a><p>Tons of free high resolution stock photos with no strings attached.
Money saving tip:
Always Google for "(company) coupons". Stock photo sites almost always seem to have deals for either more credits or discounts.