I'll second Venkat's choice of the Squeezbox.
However, the Sonos is an overpriced piece of equipment for what it aims to do. If you're going for a Sonos (~$1000), it is better to use a Popcorn Hour(~$180)/Linksys/Dlink Medialounge(~$150) units, along with a Beresford TC-7510 (~$200) or Gefen DAC (~$75) to achieve similar quality multiroom music streaming, at a fraction of the cost. If you add a wireless router at $50, the total setup for one room comes to ~$450, which is less than half the cost of the Sonos. The Popcorn Hour and Medialounge also give you the option to stream video over the network, which is a good bonus.
Sonos seems to be aimed at people who want ease of setup and wireless use. Along with Sonos, Yamaha also makes a similar, overpriced (2 lakh?) home streaming solution, again for audio only.