'When our lips speak together', a beautiful piece on forging a new language for understanding female identity. Taking the premise that masculine identity - and therefore language - presupposes phallic singularity (The 'I' of discourse) Irigaray develops the foundation for language based on dualism or multiplicity using imagery of the vaginal and facial lips.
The Cornell edition of Speculum was a constant companion, and this book provides a great core understanding of Irigaray's thinking, making it a great go-to book.
Luce Irigaray, in my opinion the most important female centered philosopher. She has been the central voice throughout both my undergraduate and postgraduate writings.