This has probably been linked in this thread before, but it is worth linking again - extremely useful if you want to go for high population.
Note that isn't the only way to play by any means (some people get disheartened after seeing the level of attention to detail required to get a massive city to work right). My larger cities are making a whopping -$50,000 an hour, but their production infrastructure is so good that the net profit for the month is typically around $5,000,000. Was able to build the great work in my region basically alone.