Apex Address compound type, based on that provided in Spring'14 for Salesforce API, http://www.salesforce.com/us/developer/docs/api/Content/compound_fields_address.htm

Address.cls

public class Address
{
	// Internally used to determine if valueOf method should read the state and country picker fields
	private static Boolean stateAndCountryPickersEnabled = false;
	
	static
	{
		// Are State and Country pickers enabled in this org?
		Map<String, Schema.SObjectField> accountFields = Account.sObjectType.getDescribe().fields.getMap();
		stateAndCountryPickersEnabled = accountFields.containsKey('BillingStateCode');
	}
	
	public String City;
	public String Country;
	public String CountryCode;
	public String State;
	public String StateCode;
	public String Street;
	public String PostalCode;

	/**
	 * Fields on the Account object that contain address information
	 **/
	public enum AccountAddress
	{
		Billing,
		Shipping
	}
	
	/**
	 * Fields on the Contact object that contain address information
	 **/ 
	public enum ContactAddress
	{
		Mailing,
		Other
	}

	/**
	 * Extract address information for the given fields from an Account
	 **/
	public static Address valueOf(Account account, AccountAddress address)
	{
		return valueOf(account, address.name());
	}
	
	/**
	 * Extract address information for the given fields from a Contact
	 **/
	public static Address valueOf(Contact contact, ContactAddress address)
	{
		return valueOf(contact, address.name());		
	}
	
	/**
	 * Constructs an Address instance from a given SObject
	 **/		
	private static Address valueOf(SObject sObj, String fieldPrefix)
	{
		Address address = new Address();
		address.City = (String) sObj.get(fieldPrefix+'City');
		address.Country = (String) sObj.get(fieldPrefix+'Country');
		address.State = (String) sObj.get(fieldPrefix+'State');
		address.Street = (String) sObj.get(fieldPrefix+'Street');
		address.PostalCode = (String) sObj.get(fieldPrefix+'PostalCode');
		if(stateAndCountryPickersEnabled)
		{
			address.CountryCode = (String) sObj.get(fieldPrefix+'CountryCode');
			address.StateCode = (String) sObj.get(fieldPrefix+'StateCode');
		}
		return address;
	}
}

AddressJSON.cls

public with sharing class AddressJSON {

	public static void demo()
	{
		// Query Account and approprite fields
		Account myAccount = 
			[select Id, 
				BillingCity, 
				BillingCountry,
				BillingCountryCode, 
				BillingPostalCode, 
				BillingState,
				BillingStateCode, 
				BillingStreet 
			 from Account
			 where Name = 'Burlington Textiles Corp of America' limit 1];
		
		// Create a Billing Address
		Address billingAddress = 
			Address.valueOf(myAccount, Address.AccountAddress.Billing);
		
		// Serialise it via JSON
		String jsonBillingAddress = JSON.serialize(billingAddress);
		System.debug(jsonBillingAddress);
	}	
}