Our corporate rate is 35% (although it is actually much less in reality because of all the loop holes that corporations exploit). I'm not sure what our top income tax rate is but it's roughly around 40%. We have not VAT tax but we have a sales tax in most states which is much lower than 21%.
I would say in terms of rates, Greece and the US are roughly the same with Greece a little higher. However, with all their tax dodging, Greece's effective tax rate is probably only a little higher than the US's. The reason Greece is in this mess is because of all their deficit spending and their lack of reserve currency status that the US has. Also, joining the Euro caused all sorts of structural monetary level problems for them. It made their exports higher priced but made buying debt cheaper. Result: less income, more debt.