Standard way to reverse a motor?
Whenever I have done motor control it has been with an H-Bridge.  But the ideal solution depends on several factors:  

What is the voltage/current required?  For &lt;24 volts and &lt;5 amps, an H-Bridge is normally the preferred solution.  The reason for this is the MOSFET's that can handle those voltages/currents are easy to get, easy to design with, and fairly inexpensive.

Is speed control, dynamic breaking, or regenerative breaking required?  If so, an H-Bridge is again usually the best.

But in the case where there is no speed control, and the frequency of "direction reversals" is low, and/or the voltage/current is very high then a relay could be a good choice.  

The main selling point of the relay is its simplicity and ease of use.  An H-Bridge will always perform better but it is harder to design, sometimes can be more expensive, and adds complexity that is not always required.