Your book cover is one of the most important aspects of marketing your book. However much time you spend on getting people to your book sales page, they won't download a sample or buy the book if the cover isn't enticing.
I absolutely recommend that you use a professional for your cover design in order to make it the most effective for your book. As an author, you don't have all the skills needed to create a great book and this is one area you can't skimp on. Pro editing is the other one you should be spending money on.
Below are some designers I recommend and at the bottom of the page are a number of articles about the book cover design process that might help with your own.
Book Cover Designers
Many of these guys are busy because they are so good, so make sure you book in advance for any covers.
Damonza 
– Books made awesome, specialist book cover designs for bestselling books. You can also get 5% off by using promo code: TCP5 on checkout.
Reedsy have a marketplace of vetted book cover designers, with experience in every genre. Click here to check out their options.
Ebook Launch Cover Design: Beautiful cover designs for ebook and print
Author Packages – ebook and print book cover design, plus formatting services
JD Smith Design: Jane is my current designer as well as doing my interior formatting. She designed Stone of Fire, Crypt of Bone and Ark of Blood, as well as some of my non-fiction books.
Derek Murphy at Creativindie Book Covers : Derek did some of my earlier covers – Desecration, Delirium, A Thousand Fiendish Angels & my non-fiction books Career Change and the original How To Market A Book. He doesn't do much design work these days, but he has also written this article on How to create your own book cover in MS Word which can help if you're cash-strapped.
Books Covered. Design agency creating market-leading book cover design.
Dream Up from DeviantArt community: You can find great designers here for any creative project
Ant Puttee at BookCoverCafe.com: Ant is an artist and graphic designer and can do some really special custom work
Carl Graves at ExtendedImagery.com : Although I don't know Carl personally, he does Joe Konrath's covers and also has some sales on ready-made covers now and then which is a great idea to keep costs down.
Jessica Bell – Book cover design services for indie authors, email support and iterative design. Discount for members of the Alliance of Independent Authors.
Cover Design Studio: Need cover design on a budget? Customize template book covers for your books.
Robin Ludwig Design: Robin does book design for some friends of mine so I can recommend her services.
Mars Dorian does ebook covers that stand out for $150-$200
Dane Low at Ebook Launch does ebook cover design for $99 – $279 and is #1 on Smashwords recommended designer list
Syd Gill – graphic design and book covers
Alexandra Brandt – Cover design (and more) for all flavors of sci-fi and fantasy.
BEAUTeBOOK – Includes ready-to-go and custom covers
Book Designer Fiona Raven – Fiona is a freelance book designer providing worry-free book design for authors worldwide. She specializes in working with first-time authors who are self-publishing.
Octagon Lab – Book cover design, logos and banners
Scarlett Rugers book design agency – Great cover designs and useful articles for indies
Book Design by Ana – including urgent designs and budget options
Karrie Ross Book Cover Designer – print, ebook plus interior design
Streetlight Graphics – cover design, formatting and typesetting, print media and other art
I do book covers – includes tips for indie authors
Covertopia – bestselling predesigned covers
Cover my book – includes premade covers for lower prices
Best cheap book covers – beautiful covers for independent authors
Hazel Lau at Kindle Station
Audria Wooster at Design by Indigo. Over 20 years' experience.
Candescent Press. Recommended by a student of mine. Design and formatting.
Digital Donna Affordable book cover design.
Joshua Jadon, Book Cover Design
Junriel Boquecosa, Graphic Design
Epicenter Creative Branding by Design
Eden Graphics, Book Covers and more
Kingwood Creations, Affordable pre-made book covers
DesignOnClick.com Book cover design and more
Hampton Lamoureux Book cover design and more, with a specialty in dark fantasy, sci-fi, and mystery
Grace My Cover Book cover design and more
WordSugar Designs. Professional graphic design for authors by an author
The Book Cover Designer The largest selection of pre-made book covers online.
Brandi McCann, Book Cover Designer
Bienvenido A. Swinton Jr., Book Cover Design
Sanja Gombar Book Cover Design For You
Burak Ulker Book cover examples here.
Breeze Books Book cover design without the breeze.
Hudson Valley Book Design Ebook and Print covers
Elena Dudina Book and CD cover design
dePinho Design Small but mighty graphic studio with a nose for design
Sam Wall Book cover design and art work
Van Garde Imagery Book interior and cover design
Dissect Design Bespoke book covers
Andrea Reider Design Graphic Design and Editorial Services
You can also check out the monthly eBook cover design awards at TheBookDesigner.com and find designers that you like there.
For lots more options, check out 99designs, where you can get all kinds of designs for your author business including book covers, merchandising, branding and business cards, illustrations and artwork and much more. You can get a Powerpack upgrade which gives your project more chance of getting noticed by going to: 99designs.com/joanna
This is a great post to help with making sure your 99 Designs project is optimal: 15 Hard Lessons Learned from my 99Designs Competition by Bryan Collins
Split testing your book cover design
One of the issues with book covers is deciding which one you think will sell best. A great way to decide is to split test them with people who don't know you or want to protect your feelings š Check out Pickfu for a quick and easy way to test.
Articles on Book Cover Design
Book cover design, the process explained, with Joel Friedlander
Book design elements and interior formatting with Jane Dixon Smith
Book cover design and entrepreneurship with Derek Murphy
How to make your own book cover design in MS Word
Podcast: Book design with Joel Friedlander
Book cover design tips with book cover designer Ant PutteeĀ
Understanding fonts and typography – from The Book Designer
Check out the Book Cover Design Awards at TheBookDesigner – you'll get some great ideas and also you will find established and new designers there