Where is a website where I sell downloads of my digital photos without creating my own website?
I know about several market places but they charge around 30% which I consider too high.
Please take this as gentle constructive criticism, since that's how it's being offered.
You don't want to invest in your business because you don't want to build or run your own web site. You don't want to pay someone else to do that for you, because you think they charge too much.
I do think you need to take a step back and do some research into the realities of the photography business, because your view seems a bit naive. There's no free lunch. Selling photos is a business. You have to invest in that business to get returns back out of it. There are literally tens of thousands of people out there with web sites wondering why nobody is buying their images. the web site is just the beginning of running a successful photography business. And having images is the easiest part of getting started.
Photoshelter has some new free publications that talk about the business and what to expect if you're going to dip your toe into it. You should check them out.
But if you think you're going to just stuff some pictures somehwere and sales will happen by magic, you're setting yourself up to fail. This business is tough and requires a lot of work. Taking professional-quality pictures merely gets you to the starting line. I'd slow down and figure out why things are the way they are out in the big world out there and why those folks are taking that 30% before you waste your time and energy doing things that won't work...
If you have not sold photos before, and therefore have little 'reputation', following or established photography business, I suggest you submit a few images to istockphoto.com. iStockphoto.com pays a royalty of 15% each time one of your images is 'purchased'. The returns are tiny, but the benefit to you is that it costs you nothing, and you will begin to learn what it takes to make commercial images (at least for stock photos).
To sell your images online, without building a website, I suggest the following as a place to start exploring:
Smugmug and Zenfolio are tools that provide you a place to exhibit your images, as well as sell them directly. Both allow digital download, but are more oriented toward prints. Neither require web skills, but better websites are possible if you have them. They are around $100 per year or more.
ExposureManager is a site that is designed more for selling images, oriented toward the business of photography. No web skills are required, but it is about $25 per month.
Newer sites are popping up all the time, including Stocksy and others designed more around the photographer than the buyer, with better rates.
Good answer by @cmason. A bit more clarification around Zenfolio and Smugmug (I used SM for the past few years and switched to ZF a few months ago):
I don't use this personally, but I hear good things about it and it looks like it fits your pricing needs as well.