Great Vipassana Mindfulness teachings - although meant for Bhikkhus these teachiings on Kammathana Forest tradition applied Vipassana Mindfulness meditation as well as Dhamma Dhesanas are useful to serious practitioners.
Click on the links to download and listen. Thanissaro Bhikkhu is perhaps for my opinion one of the most astute teachers as far as clear explanation of techniques of practise go.
Breath meditation
True friends and False Friends
Breath by breath
Analysing the breath
The End of Uncertainty
The Lotus in the Mud
An island in the Flood
Stay with the Breath
The Luminous Mind
Karma Not Self
Here is a playlist of more dhamma talks too