www.donzolidis.com - lots of monologues and scenes for student actors. Great spot for class material.
www.theatrefolk.com - shorter scenes for monologues and scene work. Great for auditions.
www.monologuearchive.com - excellent collection of classic monologues for men and women. Great for auditions or classwork.
www.themonologuearchive.tumblr.com - full of links to monologues from various locations.
www.theatrehistory.com/plays/monologues.html - lots of monologues. Mostly classical in nature.