I love covers, but I’m a tinkerer… I can’t stand to leave the covers alone for long!
For my alien cadet series, I’ve settled on two sets of covers that I really like, so I use one for paperback – I think it looks really nice with the matte covers! – and the other for ebooks. They’re a little less nuanced, but they work pretty well at thumbnail size on Amazon, which is what I wanted.
I’ve had the privilege of using art and photographs from several artists on pixabay.com. There’s a great community there, everyone I’ve interacted with has been very helpful. Everything posted there is creative commons (meaning it can be used freely), but if you want to use something commercially, it’s always good to check with the artist first.
If you’re also an indie writer, I also want to plug goonwrite.com, where I’ve gotten a couple great pre-made covers. Very reasonably priced and great work.