If you're going to build a city or town, here's a list of ideas.

Factory
Brewery
Farm
Cathedral
Church/Chapel
Cemetery
Hospital/clinic
insane asylum
nursing home
Hotel
Transportation
- airport
- train station
- light house and sea port
- parking garage ---
Warehouse
sewers
Power plant
City hall
Fire station
Police station
Prison
Courthouse
School/college
Library
Gym
Museum
Theater
Sports stadium, field, arena, etc
Zoo/ Aquarium
Barber Shop/Beauty Salon
Book store
Restaurant
- pizzeria
- bakery
Store/shopping mall
- sporting goods
- pharmacy
- grocery store
- toy store
- clothing store
- furniture & home improvement
- electronics & multimedia
Gas station
laundry place
Car wash
Mechanic
car dealer/autostore
Residential housing
Beach
Park/Playground
Ski resort
construction site

If you're looking for something that's functional and practical, here's probably the most important:
Farm (any kind)
Arena
Weapons & Armor Shop
Library (for enchanting)
Brewery (for potions)
Pet Store
Builder & Redstone Shop