Some of my favorite answers:
http://stackoverflow.com/questions/1857244/np-vs-np-complete-vs-np-hard-what-does-it-all-mean/1857342#1857342
http://stackoverflow.com/questions/2111857/why-do-we-need-boxing-and-unboxing-in-c/2111905#2111905
http://stackoverflow.com/questions/2127540/can-anyone-explain-this-algorithm-for-calculating-large-factorials/2127557#2127557
http://stackoverflow.com/questions/1988804/what-is-memoization-and-how-can-i-use-it-in-python/1988826#1988826
http://stackoverflow.com/questions/17110918/primitive-cast-and-assignments-in-java/17111090#17111090
http://stackoverflow.com/questions/17762000/mapreduce-how-to-anonymize-a-columns-values/17764505#17764505
http://stackoverflow.com/questions/17800348/how-does-java-know-where-to-jump-to-when-breaking-out-of-a-loop/17800606#17800606