Created by Danny Sadinoff, this site provides conversions for Hebrew and civil dates, yahrzeits, candle lighting times, Torah readings and holidays. You can also download its software and use it on a variety of platforms.
Hebrew Calendar Science and Myths
This is an interesting group of scholarly articles on the Jewish calendar written by Remy Landau that explains in great detail how the calendar was devised and operates. There are links to relevant websites as well.
Yahrzeit Calendar Calculator
“Enter the Jewish or civil date of departure and this page will return the Yahrzeit dates for the next 20 years. “