Sonos is still hard to beat if you want to build an affordable, multi-room system from scratch. Start with a £170 Play:1 and you can add more speakers as you go along, including the Play:3 and the brand new Play:5. If you're not fussed about high-res audio and would rather save a few quid, then it's hard to argue with Sonos.
If you want to stream high-res music to multiple rooms in your home, Bluesound (now in its 2nd generation) is just the system you need. It sounds fantastic, looks good and is simple to use.
The choice of products is complete, thanks to the Powernode 2, an amplified streamer, the Node 2, unamplified for hooking up to an existing system, and the Pulse, Puse 2, Pulse Mini and Pulse Flex wireless speakers. There is also the Vault 2, an all-in-one music streamer and CD ripper with 1TB of storage, as well as the Duo, a 2.1 speaker package, and the Pulse Soundbar.