Search YouTube for "Glee" songs. Set up an account, and click "Add" under the video to create a playlist to listen at any time. You can make your playlist public to share with other "Gleeks" as well.
Visit the Pandora online radio station. Type "Glee" into the search box. Pandora will play songs from "Glee" as well as similar-sounding music. AOL also offers a soundtrack radio where you can find "Glee" songs to listen to as well. Click "Listen Now" to stream the music over the Internet for free.
Visit Hulu. Search for "Glee" clips. Often just the songs appear, and you can play them for free. Keep in mind these clips change from time to time and are often the most current songs. Older songs are only available with the Hulu Plus subscription that costs a monthly fee.
Visit Jango's Glee Cast page to listen to free Glee music online. Click "Play Now" to listen to a variety of songs from the show. The songs are not limited to any specific season.
Visit "Glee Club Online" to listen to free Glee music on the Internet. Not only will you find videos and music files of the songs, but an extensive description of each episode (with photos) as well.
Open iTunes and download Glee podcasts. From time to time, podcasts include song snippets or whole songs, depending on who is hosting the podcast. You do not need an iPod to listen to podcasts (but you do need iTunes). You can listen directly from the saved file on your computer. Select podcasts like "Gleeful Podcast" can be download or listened to through the official website of the podcast.