Recently I downloaded and sampled 20 or so "Mindfulness" apps for my iPhone/iPad...here is a brief review of several that I think are stellar among the crowd.

Mindfulness Meditation from Mental Workout

No excuse for not meditating now...its right in your pocket. A modern way to learn and enjoy mindfulness meditation - and it's always there for your breaktime or outdoor practice. The 6 different-length mindfulness meditations and relaxation exercise are written and narrated by Stephan Bodian, author of the Meditation For Dummies®.

Bodian also has several other great apps including:

Freedom from Stress, Happiness and even one about Fear of Flying.

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Headspace (on-the-go)
This one is my personal favorite. Andy Puddicome and his team deliver a "bite size tools daily" to help you create a calmer, happier mind. A sophisticated, simple and graphically appealing tool that might aid you in developing a daily mindfulness practice. Check it out! And don't forget to watch the intro videos...they are quite brilliant.

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Zen Insight Timer
A simple trusty tool I've used for years to set the time for meditation practices. Your choice of bells, you set the time. All you have to do is turn it on and jump into the adventure of taming your mind! Even offers a 'halftime' bell so you know how far you've gone. Small price, great tool.

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Mindfulness (MindApp)
iPhone only. Another good one that allows you to set reminders, has a decent 5 minute body scan and also allows you to track your practice statistics (week, month year). Not quite as zippy as Headspace but still a solid basic mindfulness app that might help get you on track with your practice.

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Breathe2Relax
This is an interesting instructional app about diaphramatic breathing and it's effect on lowering stress. It allows you to set the length of your inhale and exhale with audio prompts, breath metronome and visual prompt options. Check it out. A little deep breathing never hurt anyone!

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Buddhify
My friend Lynette recommends this one. Looks like a very well thought out and useful tool. Can't wait to check it out. Thanks Lynette!

NEW: Updated Sept. 2012 (apps that I haven't tried yet but look interesting): 

Meditation: Mindfulness Made Easy (xinsight)

Meditation with Shinzen Young