UCLA Mindful Awareness Research Center
UCLA has an amazing program dedicated to mindfulness and they offer free guided meditations from some of the leaders in the meditation field.
The online presence for Mindful magazine, this website has articles and techniques to increase your arsenal of mindfulness tools and understand the science behind them.
Unstuck is great when you are having trouble with a decision. It helps you go step by step and offers different ways to approach this issue that can help you take the next step.
Happify was created by Dan Harris (an anchorman that had a panic attack on live television which launched his interest in meditation) and provides several programs with daily activities that improve overall well being and introduce meditation. If you are looking for help implementing a daily practice, this is a great resource.
Calm has soothing natural backdrops and guided meditations for sleep, anxiety, eating and more. If you just want guided meditations, this is a great app for that.
Pacifica also has meditations but also includes a daily mood tracker and a thought traps section that allows you to write down and challenge your negative thoughts using the principles of cognitive behavioral therapy