Roku M500, M100 or M2000 are good if it is just music you are after.
The M500 doesn't seem to be available outside the US but I use M1000's and they have been very reliable. About £100-150 on ebay. They also look really slick. You would need to hook them up to a set of powered speakers (the space saving option) or a set of standard speakers via an amplifier. They can work wirelessly or as part of a wired network. My house is cabled so I haven't used them wireless but like I say they are very good and stable. I don't know a lot about wireless stuff so don't know how the link up would work but the units themselves are good IMHO.
There are a few cheaper options, the Netgear MP101 springs to mind. Trouble is it is shit. It constantly drops the server and hangs even on a wired network and needs restarting, I imagine it would be even worse wirelessly. Also it looks shit. But if you can cope with the frustration of rebooting and such like then it is a lot cheaper (£40-50 on ebay last time I looked). I started using one of these but very quickly changed my plans...
There are also other media players but some of them need a TV screen/monitor to allow you to scroll through the menus, which I guess would not be great inyour small kitchen?
Personal preferenc is for the Roku.