Sometimes, all it takes is a few extra minutes to earn money. If you make it a habit to spend your downtime completing micro jobs, you can make a decent payout each month.
Amazon Mechanical Turk Thousands of jobs posted (called HITS). Can be anything from image tagging to transcription. Open to international candidates, too!
ClickWorker Writing, editing, and web research are the most common tasks found here. Payments are made once you reach $10.00. Also open to international candidates.
Crowdflower With 5 million contributors and growing, Crowdflower is a trusted source of micro jobs. There's opportunity to gain access to higher paying jobs once you become a ‘Skilled Contributor.'
OneSpace When you join the OneSpace you'll have access to tasks like tagging and writing. After you pass skills tests, you can work on higher paying jobs.