Mark Williams, a professor at Oxford University, offers a collection of free audio meditations. All of the meditations are taken from the book he wrote in collaboration with Danny Penman: Mindfulness: Finding Peace in a Frantic World. 

I have used a number of these meditations with my own clients over the years. Many have commented on how the practice helps to calm their racing minds and feel more centered in the present moment.

Free Audio Mindfulness Meditations by Mark Williams