This method is only known to those who do it, and they mainly avoid sharing this information just to reduce competition. If you're a good listener with good typing speed then transcribing audio into text can get you a good amount of money.
Transcription jobs allow you to work from the comforts of your home without any investment. The more you work, the more money you earn.
Following are some of the best sites to earn by transcribing audio into text:
1. Quicktate: Convert audio files into text by following their guidelines. They pay 1/4 to 1/2 cent per word depending on the audio type (General or Medical). Read More
2. Scribie: Pays $1 per 6 minutes of audio transcription. The pay is very less, however, once you gain experience you can earn more. Upon signup, Scribie will inform you via email if your application is accepted.
3. SpeechInk: To work with SpeechInk you need to have mTurk account. That's where they post assignments. Update: It's now changed to SpeechPad.
You only need to have a good pair of headphones along with an Internet connection to start Transcribing.