The main place is on the "Dashboard" page. Look on the right side at the box labeled "Proposals Received." You'll see a list of your proposals, listed with the most recent at the top. You can even respond to these proposals by clicking them here and pressing the "Decline" or "Accept" buttons.

You can see a larger, easier to navigate list by clicking the blue "View All Proposals" link in the top-right corner of that box.

Alternatively, you can go to your "My Projects" page and visit the "Posted Projects" tab. Find the project post that you want to see your proposals for and open the Proposals tab to consider and compare them.