Over the last couple of years, I've written about how important it is for an indie author to have a good cover for their book. I've invited several indie authors here to talk about the process they went through to get their covers, whether doing it themselves or hiring a professional. M. Terry Green pointed me in the direction of affordable, professional designers who offer pre-designed and customizable covers—the growing list can be found by clicking on our "Book Cover Designers" tab.
While we've seen a decrease in the number of bad covers submitted here, there seems to be no shortage of lousy covers out there.
So I'm going to throw another resource at you:
CoverCritics offers a snark-free environment (the host, Nathan Shumate, prohibits it) where indie authors can receive constructive criticism of their book covers before they go to press. I'm heartily recommending that any indie author who designs their own covers, isn't sure about a cover they purchased, or just wants some feedback submit it there (it's free) before publication. When you visit the site, you'll see from the comments what's good or bad about the designs. And actual graphic designers are among the commenters. Even if you're not at that stage yet, you'll learn a lot from what's discussed there.