omnidirectional antennas and the dipole antenna This article on Cisco's website is the clearest explantion of omnidirectional antennas I've found. What isn't so clear to me is... 1) Why is the dipole antenna the most common design for omnidirectional antennas? 2) For example, why not have an antenna that has a power source on one end, and then emits current to the other end? 3) Also, why does the radiation pattern (given on the linked page) take an odd spherical-like shape, instead of say, a cylinder?

The dipole antenna is the most common because it is inherently simple and very inexpensive to produce.

Your example, doesn't make much sense, beause that is exactly what is done with all antennas. You have a power source (the transmitter) on one end. The signal is radiated based on the shape of the antenna and any characteristics of the antenna to focus the signal.

As to why a dipole emits an "odd spherical-like shape" (often referenced as a toroid or doughnut), that is a relatively simple concept. A dipole antenna is often just a straight piece of wire. The amount of surface area available directly relates to how much signal is transmitted in any direction. You have a much larger surface area around the lenght of the wire than you do at the tip or base, allowing much more signal to be radiated from the sides.