If anyone has any good online resources that deal with thangka iconography and explain in depth each element and being let us know.
Other than the Handbook of Tibetan Symbols and Motifs
by Robert Beer which has already been mentioned, the best resource I've found online by far is the Facebook page for the Munsel Thangka School of Art.
The school's founder and main instructor, Kim Chong, posts teachings about the various elements of iconography pretty regularly in an effort to educate the masses on the deeper meaning of thangkas. She is a devoted student of several Karma Kagyu lamas, including Khenchen Thrangu Rinpoche, and specializes in the Karma Gadri style, but is non-sectarian in her wish to help spread the Dharma. Thus far she has covered many subjects, including but not limited to:
Five Buddha families
Peaceful & Wrathful torma
Five sense objects
Eight auspicious symbols
Animals (steeds, trampled & background)
Flora (lotus, utpala, wish-fulfilling trees)
Jewels (wish-fulfilling & otherwise)
Peaceful deity implements (malas, etc.)
Weapons of the Peaceful & Wrathful deitieshttp://www.facebook.com/munselart
Here's a sample of what you can come to expect from Kim-la. The following is her most recent post, with some slight editing to clarify the English. She is ethnically Chinese and not a native English speaker, so sometimes her English is a tad broken, but it is well worth the effort to read her illuminating explanations. For those who can read Chinese characters, all of her posts include both languages...
The symbolism of the arrow is revealed in legends of the Mahasiddha Saraha [...] and his dakini consort, who was a master [arrow-smith]. Saraha is usually depicted as sighting along an arrow’s shaft. Here the arrow-shaft represents the central channel; the smoothness of the bamboo joints symbolizes the untying of the psychic knots that constrict the flow of wind into the central channel. The four sections of the bamboo shaft [...] symbolize the four concentrations, [four] mindfulness[es], [four] immeasurable states, the karmas, [the] four joys, four moments and the four levels of tantra. The sharp vajra-point of the arrowhead symbolizes the concentration of wisdom as penetrating awareness or single-pointedness of mind. The thread represents the binding of the tantric commitments. The five-colored threads [feathers?] glued at the flight-end of the shaft represent the binding of the five Buddha wisdoms, the five perfections of method (generosity, discipline, patience, effort and concentration), with the bow representing the six[th] perfection (wisdom). The two sides of the arrow’s releasing-notch represent the union of relative and absolute truth, and the union of conventional and ultimate bodhicitta. (For further information read the previous weapon teaching posts).
"The Sutras, Tantras, and Philosophical Scriptures are great in number. However life is short, and intelligence is limited, so it's hard to cover them completely. You may know a lot, but if you don't put it into practice, it's like dying of thirst on the shore of a great lake. Likewise, it happens that a common corpse is found in the bed of a great scholar." ~ Karma Chagme དྲིན་ཆེན་རྗེ་བཙུན་བླ་མ་རཱ་ག་ཨ་སྱ་མཁྱེན་ནོ།