I'll start with a more well-known entry but firm favourite...
A Lizard in a Woman's Skin (Una lucertola con la pelle di donna) (1971) - Lucio Fulci 
A somewhat difficult statement to make when considering how close this particular genre of cinema is to my heart and sensibilities, but not only is Lucio Fulci's stylish, trippy giallo possibly my favourite (well, at least of what I've seen so far) within this fine genre of cinema, but also his overall best work. Florinda Bolkan is fantastic as Carol who experiences a series of vivid psychedelic nightmares consisting of depraved sex orgies and LSD use. In her dreams, she commits a graphic murder only to awaken to the real thing, which in turn plunges herself into the middle of a criminal investigation. Whilst 'Lizard' may not be your conventional giallo it carries a unique flair and atmosphere that melds the surrealistic with the gory and uncompromising set pieces which Fulci utilised to such great effect in his later horror efforts.
Available on DVD in the UK from Optimum/Studio Canal which boasts a superb transfer and really promotes the great Morricone soundtrack.