I've just finished adding https support for Magnatune, which you can reach at https://magnatune.com.
I've also confirmed that we are not vulnerable to the Heartbeat vulnerability.
Note that graphics and audio files are not provided via https, but everything else is. All modern browsers work: I tested IE10, Firefox, Safari and Chrome. Older versions of IE (IE8/IE6) do not work with our https support.
The only bug I know about with our https support is that using the search feature takes you out of https mode. Also note that https mode is not available in the download member version of the web site. Both of these are on my to-fix list.
ps: one big motivator for adding this support was that we were accidentally listed on the "experimentally approved" list of EFF's excellent HTTPS EVERYWHERE plug in and magnatune didn't actually work with https yet!