[bencpeters]

I really like this work: http://www.epi.org/publication/raising-income-taxes/

It basically suggests that: a)top tax rates have historically had virtually no significant effects on overall economic growth

b)we are well below the optimal tax rate for maximizing revenues

The authors of the paper on which this summary article is based on go on to suggest an optimal top effective rate of 68.7% as the revenue maximizing point (basically the optimal trade-off between revenue and dampening effects and/or evasion)

I find this work pretty convincing...