Devanagari is interesting because it's a completely rationalized alphabet. The symbols are organized by phonetic type and place of articulation, in the same way a modern linguist would lay them out, and they have been for thousands of years. Speakers of languages written in devanagari usually become incredibly frustrated when learning a language written in the Roman alphabet, because of the totally irrational and apparently random order the letters. The only other alphabet I know of that has the same level of organization is the Korean hangul script.
The reason for this order is the genius of the early Sanskrit linguists, one of whom, Panini, has a legitimate claim to being considered the greatest linguist of all time.