Starting with A:
* Atlanta
* Aurora
* Amarillo
Starting with B:
* Baltimore
* Birmingham
* Buffalo
Starting with C:
* Chicago
* Colorado
* Columbia
Starting with D:
* Dallas
* Denver
* Detroit
Starting with F:
* Fresno
* Phoenix
Starting with L:
* Louisville
Starting with M:
* Miami
* Memphis
Starting with N:
* New Orleans
Starting with O:
* Omaha
Starting with P:
* Portland
Starting with R:
* Reno
* Rochester
Starting with S:
* Seattle
* San Diego
Starting with T:
* Toledo
Starting with V:
* Virginia
This is not an exhaustive list, but it provides a good starting point. There are many other US cities with three syllables.