I don't know where you're from, or how many times you have been in Southern California, but Newport Beach is unique. Unique enough that the ride to see the sights is far different than to do a ride.
You're going to want to ride and explore. That means stop and go. If you want a long stretch, Newport Beach is a place you want to go through, but not at. For a 50 miler, try Huntington Beach pier at Main street, all the way down south on Pacific Coast Highway (PCH) to Dana Point Harbor and back. You'll get lots of ocean views, expensive neighborhoods, and a good mix of elevation. Fourth of July week might be a bit crowded on PCH.
There will be several bike shops along the way. The one in Laguna Beach on Thalia did rent road bikes, but you'll have to call them.
Last edited by Garfield Cat; 06-14-10 at 08:10 AM.