Should you even try to make your own book cover? This post by June Stevens Westerfield may help you decide.
Next, you may want to take a look at Amazon's criteria for Kindle book covers and paperback book covers to make sure that yours will meet the requirements.
Author Tamie Dearen has compiled a list of sites where you can find free images to use in book covers or other designs.
My Book Cave has a two-part series on book cover design. Part 1 is about picking the right image, and part 2 deals with setting up your file and image.
Author Bruce Fotler has a great article about his "book cover blunders", with mistakes for newbie cover designers to avoid. He includes links to other helpful cover-related sites.
YouTuber Derek Murphy has a video about 7 must-have qualities for a book cover that sells. Make sure to check out his link under the video if you want more video options about cover creation.
The same Derek Murphy also has a useful list of specific fonts that work well on book covers, organized by genre.
Perry Elisabeth has a great blog post about those fonts and how to use (and not overuse) them on covers.
And, Derek Murphy has an article listing cover design "secrets" that can be used to "manipulate" people into buying books.
Starla Huchton, herself a cover designer, has a great article with some quick tips for cover design.
She's also written an article about the costs of a good cover, and how to end up with an affordable one.
Canva is a great site on which you can create your own cover for free.
These people give instructions for how to create a cover using Microsoft Word or Photoshop.
Want to get elaborate? Here is Derk Muphy's explanation of how to create an animated (gif) cover for your ebook!
Want to put several books together into a boxed set, but unsure how to make your existing cover work for that? Lisa Shea explains how in this article. Indies Unlimited has another explanation of how to do it using Gimp.
Have you made a cover, but you're wondering if it's any good? The Rate My Kindle Cover site will let you upload it and get feedback (for free!) before you publish your book.
Have you made two or more variations on a cover, and you want opinions from your friends, family, or the fellow authors in your writing group on which one is better? Stephen Oram explains how to use a survey to choose.
This article, and the accompanying infographic, covers the topic of book cover design thoroughly (including what to do if you decide to work with a cover designer).
Finally, here are some book cover artists you can contact if you're looking for someone to design the perfect cover for your own book. Note that some of them have specific styles or focus on specific genres, so you'll want to choose carefully as you consider what will work best for your book - and of course your budget.
Affordable Book Covers and More
Blue Valley Author Services
Book Cover Bakery
Cover Shot Creations
Deranged Doctor Design
The Design in Your Mind
E Kaiser Writes
Fury Cover Design
Paper & Sage
Perry Elisabeth Design
Psalm 40 Publishing Services
Time Keeper Art
And if you're planning to work with a cover artist, don't miss Joel Friedlander's tips, or Starla Huchton's blog post on that topic.
I hope these tips are helpful! If you have any other cover artists to recommend, or if you know of any other useful articles on the topic of cover creation, please feel free to mention them in the comments! You're welcome to share tips of your own, too.