Music players like iTunes and Winamp can be used to create something like spaced repetition for the music you have on your computer, since they let you create smart playlists based on criteria like playcount and when a track was last played. So you could create your spaced repetition playlist which keeps tracks out of rotation after you play them, but puts them back into rotation sooner if they have a lower playcount or a higher rating. For instance, it could include tracks with:

Playcount of 3 or less, and not played in last 1 day OR
Rating 5, playcount 4-6, and not played in last 3 days OR
Rating 4, playcount 4-6, and not played in last 6 days OR
Rating 3, playcount 4-6, and not played in last 12 days OR
Rating 5, playcount 7-9, and not played in last 7 days OR
etc.

Of course you'd have to figure out what numbers to use and program it yourself (and you'd have to rate everything you listen to, if you want to use rating as one of the criteria). Then you could listen to that playlist on shuffle, or choose what tracks to listen to while limiting yourself to the tracks on that playlist.

I actually have a crude version of this system in place, which I use to listen to my music on shuffle. It started as something much simpler (I put a one-week delay in for everything because I didn't want tracks to come up in the shuffle a few days after I'd listened to them), and over time I've lengthened the delay and added some dependence on rating & playcount.

Try Pandora? Their licenses prevent them from playing songs too frequently, but they replay songs you upvote more than songs you don't (and never play songs you downvote), as well as learning from your preferences to give you new music you might enjoy.

I have found that their selection can be somewhat limited in some subgenres, to the point where you can have upvoted or downvoted enough that it no longer has new music it thinks you'll be interested in. (So far, I've only done this with Celtic Punk, and that was made easier by my dislike of The Pogues.)