I think I’ve bought from 7digital a time or two in the past and had no problems. Obviously there are issues with Amazon as a company, but I think they were the first big name to offer DRM-free MP3 purchases and I used it a lot back when it first launched, especially since they offered a selection of albums each month for just $5. They should have most mainstream music available for purchase, depending on which country you’re in. According to this Wikipedia page listing music stores they only offer 256 kbps MP3 but I was sure most if not all were upgraded to 320 kbps now, although of course you would have to re-download anything if you had downloaded the lower-quality version previously. That Wikipedia page is a good link to other stores as well, with a number I’d never heard of including specialty stores.

Also, along with someone else’s comment mentioning ripping CDs like the old days, check to see if you have a local record store. It’s been a mantra since at least the Gen-X days to “support your local scene.” I know in Raleigh the longtime staple Schoolkids Records is still alive and kicking, although their Chapel Hill store closed last year. It might take some digging but it can be worth seeing if there’s a local store in your area.