I've always considered it a huge help when getting to know a person to read the books that are important to them, and to try to unearth traces of their philosophy, ethics, personality or mode of expression in the characters. Maybe it's the English major in me, but I've always had the greatest success understanding people by analogy with fictional characters.
I don't know if any of you are like that, but here (in no particular order) is a list of characters with whom I identify deeply:
Alia Atreides, Dune
Stephen Dedalus, A Portrait of the Artist as a Young Man
Atalanta, Greek mythology
Tullus Aufidius, "Coriolanus"
Sansfoy, Book I of The Faerie Queene
Britomart, Books III and V of The Faerie Queene
Tybalt, "Romeo and Juliet"
Mr. Lawrence, The Tenant of Wildfell Hall
Brienne of Tarth, A Song of Ice and Fire
Therem Harth rem ir Estraven, The Left Hand of Darkness
Cassius, "Julius Caesar"
Rogue, "X-men" comics
Valentine Michael Smith, Stranger in a Strange Land
Storm, "X-Men" comics
Tyrion Lannister, A Song of Ice and Fire
Nightcrawler, "X-Men" comics
Two, Delia Daella and Raquel, Tales of MU
None of these characters is explicitly autistic. Many of them have something going on that approximates an aspect of my experience of autism (say, Rogue's inability to be touched, Alia's unique mental abilities, Atalanta's feralness, Stephen Dedalus's powerful imagination, fierce creativity and intellectual isolation, Two's literalness), but obviously the analogy is always going to be imperfect.
I have only encountered four autistic characters in novels: Lou Arrendale in The Speed of Dark, Crake in Oryx and Crake, Blackwolf in Soon I Will Be Invincible and Christopher Boone in The Curious Incident of the Dog in the Night-Time. Of those, Blackwolf and Crake both struck me as ciphers. They weren't autistic characters so much as they were opportunities for their authors to use autism for their own metaphorical purposes.