I got a flier from monoprice.com today that mentioned some thin Ethernet cables in multiple lengths and colors. If you are thinking about wiring your Sonos system one of these cables might be less visible than an older, fatter cable.
Cat 6 - https://www.monoprice.com/product?c_id=102&cp_id=10232&cs_id=1023205&p_id=13538&seq=1&format=2
Cat 6A - https://www.monoprice.com/product?c_id=102&cp_id=10260&cs_id=1026003&p_id=27400&seq=1&format=2&cl=res
Cat 6 is likely more than you need for Sonos but I didn't see any Cat 5E cables like these there. Possibly on other sites too, maybe cheaper?