Well, what about a tax (around 0.5%) on every transaction through the banking system? Technically, it would be no different than the usual calculations of changes and fees that banks apply to all their transactions, and would use existing infrastructure. This would eliminate the need for personal income tax. Humans would no longer be taxed on their income.
In my opinion, governments could raise additional tax revenue from excise taxes and duties, corporate taxes, etc. while using the choice and levels of taxation to implement socially desirable behaviour.
I came across this site http://www.apttax.com/ which has an American-centric analysis of the idea.
I'd go a step farther, from my viewpoint in Brussels, and point out that this could be implemented across the countries of the Euro zone. All internal Euro transactions as well as all transactions with the outside would be subject to the APT tax. This would finally make it possible for society - human beings - to drink from the firehouse of human economic activity, by providing a way of skimming a small percentage of the total volume of transactions of the entire economy. It's the ultimate progressive tax: the more money you channel through the system, the greater your contribution to the revenue pool.
But the big behavioural win would be the elimination of having to choose between working "in black" or in the official economy. The current system, with personal income taxes, is the ultimate disincentive - if you're hard-working, the more you work, the more taxes you pay. Or you cheat. Look at the worst-off European economies, like Greece, where corruption is endemic. Once personal income taxes are eliminated, you can do whatever level of work you want to pay for your chosen lifestyle. Rich people certainly don't lose out either - but they can't bribe their way out of paying their share by the simple volume of their transactions.
What do you think?