I recently read the ebooks My True Type and The 16 Personality Types by Dr. AJ Drenth. Drenth offers the best descriptions I’ve read of the types and their functional stacks. I totally recommend these books to anyone unsure of their type. Drenth’s profiles and function descriptions/comparisons are very lucid, insightful and succinct. Doubts about my own type were cleared up after reading them. The only flaw is the obvious lack of editing (they read like a first draft) – but it doesn’t matter, and perhaps Drenth realized this and figured why bother?