Mr. Gordo's link is good, Beautiful Breath.....Berzin, of course, comes from a Tibetan-centered viewpoint, but I think it's a fair synopsis he provides.
However, in his quick summary page: http://www.berzinarchives.com/web/en/archives/study/comparison_buddhist_traditions/general/survey_basic_forms_buddhism.html
-I think you could get the wrong impression.
Those things which seem "corrupt," i.e. ritualized practices, deities, etc., need to be understood from an inner point of view. They are, in fact, nothing more than methods for the same general purpose as any meditation technique.
Any practice which takes into account the Four Nobles Truths, and the Four Seals, can be seen as Dharma. Madhyamika philosophy, emptiness, and Vajrayana practices all fall within this realm.
The four seals are--
1. All conditioned things are impermanent
2. All emotions are of the nature of suffering
3. All phenomena are empty, without inherent existence
4. Nirvana is beyond extremes
And the Four Noble Truths, perhaps more well-known, are-
1. Life is suffering/samsara
2.Attachment is the cause of suffering/samsara
3.Cessation of Samsara/suffering (Via freedom from Attachment) is possible
4. The Path to Freedom is the Noble Eightfold Path