I'm looking to start making book covers for myself and a few friends, and I am wondering what software to use. I have Photoshop and GIMP for the manipulation aspect, but what about the rest?
There are many applications that can do this. I have explained two options that you may consider:
(1) Paid Applications: (from Adobe)
a. Photoshop - Image manipulation
b. Illustrator - Vector Graphics
c. Indesign - Layout your cover page/book exactly for Print & Publishing
(2) Free Applications: (Open Source)
a. GIMP - Image manipulation
b. Inkscape - Vector Graphics
c. Scribus - Layout your cover page/book exactly for Print & Publishing
A good cover/book design is an outcome of effective use of above three tools. Hope this helps you.
You have PS or Gimp for your photo manipulation.
Then you have a vector-based programme like Illustrator or Inkscape for scalable vector work.
Then, finally, you have InDesign or Scribus as the desktop publishing programme where it all comes together.
The last two are desktop publishing programmes, and as such, are programmes commonly used to create entire books. The other four are useful/not useful entirely dependant on what sort of imagery you are going to make.
You really have in Photoshop everything you are likely to need, at least for now. If you were setting out to do this for a living, I'd steer you toward InDesign and Illustrator, but for your purposes you can (and professional designers do, in many cases, depending on the specific design) work entirely in Photoshop.
If you find you need to create sophisticated vector artwork, then Illustrator or Inkscape is the usual tool of choice.
One important thing you need to know is that if you're self-publishing, you must send a PDF file, not a PSD, jpeg or TIFF to the print service. That will ensure that any vector information in your layout (such as text) goes through the negative or plate making software (called a "RIP," for "Raster Image Processor") at full resolution.
Although the free (open source) software is fantastic you can still run into hurdles when trying to then work in CMYK as the tend not to have this colour mode in their make up yet. It could be worth considering the use of Adobe's Creative Cloud if you need to over come this issue. You will need to sign up for a minimum of a year but it will work out cheaper than buying all of the software in one hit.