in 2021
The next time May 21st falls on a saturday is in 2016.
2015
2021
As of 2017, it will be in 2018 and the next time after that will be in 2029.
Easter Saturday will next fall on April 12 in 2031.
The next time that April 16th falls on a Friday is 2021.
The next time October 31 falls on a Saturday is in 2015.
At the time of answering this question (Dec 2014), the next time will be in 2025.
May 23 fell on a Saturday in 2009 and will again fall on a Saturday in 2015.
After 2011, when the question was originally asked, the answer was 2015. The next time after 2015 is 2026.
The next time March 30th falls on a Saturday is in the year 2024. After that, it will occur again in 2030. March 30th, 2024, is notable as it is just a day before Easter Sunday, which is celebrated on March 31st that year.
At the time of answering this (2014), the next October 31 which falls on a Saturday will be in the year 2015. After that, October 31 will occur again on a Saturday in the year 2020.