Yeah, favourite books is hard. Problem for me is that my tastes have changed drastically over time, I can't think of anything from over 6 years ago that I still consider influential to me. But at the moment:
Dreams - Carl Jung
Totality & Infinity - Immanuel Levinas
The Practice of Everyday Life - Michel de Certeau
Society of the Spectacle - Guy Debord
The Third Mind - William Burroughs & Bryon Gysin
The Castle - Franz Kafka
Alice in Wonderland - Lewis Carroll
Watchmen - Alan Moore & Dave Gibbons (for turning me to comics)
The Acme Novelty Library - Chris Ware (for being the best damn comic I've ever read.
I Ching (potentially in time, I love the concepts, but haven't used it enough to say just yet.)
It sort of irks me that none of my favourite authors are female. I mostly read non-fiction, the few fiction authors I've spent a lot of time with in a while being James Joyce, Franz Kafka, William Burroughs & J.G. Ballard... I read comics very widely though, in terms of multicultural and female authors, I just can't think of any - besides maybe Lynda Barry and Alison Bechdel - who would stand out as favourites.