I remember a discussion I had with someone about this subject ages ago and can always remember the scenarios like "Romeo & Juliet", "Othello" and "Cinderella".

I spotted this from the Wollogong Pig Breeders' Gazette (where else?) discussing Irish playwright Denis Johnston's eight plots for plays :
http://ncc1701.apana.org.au/~larrikin/sfandom/fanzines/middlemissp/wpbg2.html

"1. Cinderella - or unrecognised virtue at last recognised. It's the same story as the Tortoise and the Hare. Cinderella doesn't have to be a girl, nor does it even have to be a love story. What is essential is that the Good is despised, but is recognised in the end, something that we all want to believe.

"2. Achilles - the Fatal Flaw that is the groundwork for practically all classical tragedy, although it can be made comedy too, as in the old standard Aldwych farce. Lennox Robinson's The Whiteheaded Boy is the Fatal Flaw in reverse.

"3. Faust - the Debt that Must be Paid, the fate that catches up with all of us sooner or later. This is found in all its purity as the chase in O'Neill's The Emperor Jones. And in a completely different mood, what else is The Cherry Orchard?

"4. Tristan - the standard triangular plot of two women and one man, or two men and one woman. The Constant Nymph or almost any French farce.

"5. Circe - the Spider and the Fly. The Barretts of Wimpole Street if you want to change the sex. And if you don't believe me about Othello (the real plot of which is not the triangle and only incidentally jealousy) try casting it with a good Desdemona but a poor Iago.

"6. Romeo and Juliet - Boy meets Girl, Boy loses Girl, Boy either finds or does not find Girl - it doesn't matter which.

"7. Orpheus - the Gift taken Away. This may take two forms: either the tragedy of the loss itself, as in Juno and the Paycock, or it may be about the search that follows the loss, as in Jason and the Golden Fleece.

"8. The Hero Who Cannot Be Kept Down - the best example of this is that splendid play Harvey, made into a film with James Stewart.

"These plots can be presented in so man different forms - tragedy, comedy, farce, whodunit - and they can be inverted, but they still form the basis of all good writing. The fault of many contemporary plays is simply that they do not have a plot."

to which he added the following note:
"To Denis Johnston's eight plots for plays you can add David and Goliath, the individual against the repressive/corrupt powers of the state or community, or their rival claims. As in Enemy of the People, The Visit and, of course, Antigone."

The other book which I have heard mentioned from time to time is "The Thirty-Six Dramatic Situations" by Georges Polti, reviewed here:http://www.glassner.com/personal/drama/screen/books/polti.htm