Amtrak is sold out but the Cool Breeze century is another fairly easy century if you really want to do an organized century (http://www.cibike.org/cool-breeze.html)

Of course, it's in two weeks so get training.

The easiest century advice I've seen is that if you ride a total of 400 miles in the two months leading up to your century and can do 70 in one ride, you'll be fine. No record setting, but fine.