Guatemala City:
In Guatemala City, be sure to check out the central market, the plaza, the cathedral and the palace. They are all in the same block pretty much. At the central market make sure you catch a glimpse of "Frog Man." A Guatemalan beat box legend. Makes for great entertainment!
Flores:
Flores is a small island town (colonial of course). Plan to spend a few days here if you can. It is breathtaking and has some cool bars. It is also the jumping point to Tikal.
Antigua:
Antigua is a small colonial town just outside Guatemala city, which was once the Guatemalan capital. It is placed on the Unesco World Heritage List. Right up your alley if you like your alleys to be lined with colonial architecture. Look out for Guatemala's unique squat, Baroque-embellished churches.
Other Cities:
Puerto Barrios - along the Caribbean coastline of northern Guatemala, gateway to Belize by boat
Cobán
Livingston - along the Caribbean coastline of northern Guatemala, west of Puerto Barrios
Chichicastenango - great market town
Zacapa
Monterrico
Santa Elena - twin lakeside town to Flores