Monologue choices are an intensely personal thing. You have to find ones you really connect with. In the thread "In search of contemporary contrasting monologues," Chrissyblu posted some excellent advice on searching for monologues in general.
For classical, unless you are specifically required to do Shakespeare, it might be better to choose something else, because Shakespeare is hard to do well. Ibsen, Chekhov, Moliere, Shaw and Wilde are some playwrights you might want to look at.
It's not at all uncommon for students to engage the help of a theatre professional to help them choose and prepare monologues. Ideally, you should find somebody who has worked with other students preparing for college auditions.
Search the CC Musical Theatre forum under "monologue" for further advice and ideas on coaching and other matters.