The field of algorithms is vast. Humans have been designing algorithms since antiquity, e.g. GCD algorithm. Of course, algorithms are the backbone of the current information age. Here are just a select few which have fascinated me because of their simplicity and cleverness.   

Every undergraduate course in Computer science covers a range of data structures: Arrays, Linked-lists, Trees, Graphs, and Hashes. However, there are yet more data structures, some quite well known and some not as much. Here are a few of them which I think are especially noteworthy since they are clever, minimal and quite useful.

The Linux command screen deserves to be more popular than it is currently. Here is a brief tutorial