I use Morguefile ALL the TIME! It's a huge repository of copyright free photos. You have to wade through a ton sometimes to find what you're looking for...if you need something really specific. But did I mention it's FREE? Copyright free stock photos are great for dressing up a blog post or a Twitter tweet.
Not as big of a selection. In fact, just a fraction of the selection. However, the photos are scrumptious. If you can find a use for the zanier of the lot, you will be pleased. They are big files though. Again...I use these photos for dressing up boring text. (Gasp! My text is never boring!)
3. Google Images
Caution! If you don't have filters set, you'll get an eyefull, depending on what you're searching for. I like to find popular MEMEs or sayings or posters and share them on Facebook or Twitter. You might find things unexpected too.
You have to buy Printmaster. I used to get a new copy of the software every other year or so. Then I went without for a couple years. Now I have it again, and I LOVE IT LOVE IT LOVE IT. I have been having a ball playing with my free stock photos, adding text and so on. I have only scratched the surface of what I'm going to be able to do for book promotion/blog promotion/self-promotion. Can't say enough good about the software. User-friendly, intuitive, colorful, variety etc. Fun times ahead.
1. Dollar Photo Club
Yeah, you have to pay for this membership too. The thing is, they have a truly fabulous collection, and it's almost guaranteed they'll have what you need...from potential book covers, to promotional stock photos. It's great, and at 10$ a month, completely affordable, IMO.