Both good suggestions. One more.
What receiver? Many receivers today have integrated Ethernet ports. You can share your music on your local network, and add it as a media source in your receiver. The receivers are built to recognize uPnP storage, so a standard share in Windows, Mac OSX (which shares the same as Linux with NFS), or Linux will do just fine.
I feel that is the second best option, since it typically requires no additional hardware beyond a cheap Cat5e cable. If you desire wireless, there are devices (not-so-cheap) that will convert your standard ethernet connection into a Wifi signal. These adaptors join your network via DHCP just like your laptop or computer would, so it's invisible to your receiver and computer and will work the same as hardwired networking.
I would suggest media streamers and AppleTV-types, but for the money, it's not worth it if you're only streaming audio. That's like buying a Ferrari just to commute to work 5 miles away in urban traffic.
Hope that helps.