Yes two bands, with the focus on making it attractive for people to earn money and pay tax, ideally the 0% band would be just enough to clothe, feed yourself and pay rent in a bad neighbourhood.
Progressive is a word that seems to mean different things to the left and the right, I notice you didn't define it.
As I said a flat tax is economically progressive because it doesn't discourage people from trying to earn more money.
At the moment you have people buying houses they don't need or using complex financial instruments just to do something with their money because if they don't they will get taxed more. Investing this money for the sake of it is not always beneficial to the economy or society, I favour a persons right to choose what to do with their own money.
I am coming from this from a libertarian perspective, whether you earn 50k a year or 500k the government should not be taking a higher percentage from you than other people. Especially considering that with a percentage rate whilst the proportion is the same, the actual amount of tax high earners pay is greater (which is socially progressive enough for me, but perhaps not for you). I believe I am using the word proportion correctly here, but if not please feel free to let me know how I have got it wrong.
Here in the UK the top rate of tax is 50%. I doubt I will ever be taxed at that rate but the government taking half a persons income scares me a little, no wonder people try to move their money around so the taxman can't get at it.