The open source media center solution XBMC, now soon to be ported to Windows 8, have during the last year gotten a well working spotify add-on: spotimc. Its currently in beta 4 and can be downloaded from the developers page or from this unofficial mirror. Development discussion can be found on the xbmc forum pages and the source code are maintained by the founder mazkolain at github.
Well worth testing for any fan of XBMC.
EDIT: Now SpotiMC beta 5 is available.