Though some of them are a bit overlydone, monologues (especially the off-beat monologues) from Christopher Durang plays are terriffic! One of my favorites is Jane's "Peter Pan" monologue in 'dentity Crisis.
Also if you wanna play an older woman there are some great Martha monologues in Who's Afraid of Virginia Woolf (there are also some great male monologues in the play too)
But one of my most favorites would have to be a monologue from Catholic School Girls. It's pretty funny (it's a 2nd grader explaining church to some kindergardners) here's a link to the monologue--->
http://demoening.homestead.com/Catholic.html