The 1991 Sim City game on the SNES made for some entertaining hours, trying to figure out the right formula to grow your city. The soundtrack is pretty relaxing, you can get it here.
There's not many songs in this OST, but there's some decent relaxing ones that have that nice retro, Nintendo-y feel to them.
When looking around Youtube for covers, you'll find that the covers are pretty relaxing too, like this almost jazz-like rendition of the menu theme.
It's too bad the OST doesn't seem to be that popular, a track like the Metropolis theme which is somewhat louder could easily have a rock/metal like cover.
To conclude, check out this great Piano medley.