The past decade has seen the emergence of new services--many of them free--that allow you to stream music from the Web, as well as to store your own music files online for easy access from your PC, your TV, or your smartphone.
Music on Demand
Services such as Pandora and Slacker create personalized radio stations that bring commercial-free music to your PC or smartphone. Most are free, though all reserve certain features (such as mobile access or desktop apps) to paid customers. Of the major services, Pandora is the best choice for users who want free music on their phones or streamed to their TVs via Roku or other cloud-enabled devices. Another option, Grooveshark, provides more customization by letting you search for and play specific songs on demand, but for a fee.
Social media services such as Blip.fm make it easier to share and discover music with friends through integrated Facebook and Twitter support, so you can tell everyone what you're listening to and see recommendations from people whose taste you trust.
Stream Your Own Tunes
What if you already own lots of great music, and you just want to be able to listen to it on any device? Digital music lockers can store your tracks online and stream them to your PCs, phone, and tablet.
Amazon has launched a service called Cloud Player for the Web and Android phones, offering 5GB of free cloud storage via Amazon Cloud Drive for your existing music collection. You can upgrade with options ranging from 20GB for $20 per year up to (for those who have too much money on their hands) a terabyte for $1000 per year. Upload your existing music files to Cloud Drive, and Cloud Player will stream them to your PC over the Web, or to your Android phone via the Amazon MP3 app. Android users also have the option of copying the files to their SD Card to save bandwidth and avoid streaming problems.
Earlier this month, Google launched Google Music, which works like Amazon Cloud Player but includes a desktop app. While in beta, the service is free. Final pricing has not been announced.