Perfect Contrition: If you can find it, pick up a book called [u:3iyeo5vn]Hell: The Dogma of Hell and How to Avoid Hell[/u:3iyeo5vn]. The second half of the book includes a nice section on contrition.

(From memory since I lent someone my copy of Hell and never got it back)

Bascially, Jon got it right. It is feeling sincerely and perfectly sorry for having sinned against God. The fear of the loss of heaven and the pains of hell is known as attrition. Penance is not a part of contrition or attrition but a separate matter entirely. Contrition/Attrition are for forgiveness or your sins; penance is ‘paying’ for the damage you have done by sinning.