At some point in the past I found a cancer portal site which had aggregated data for the relationships between various mutations and their prevalence in cancer types and tumor data. The data was presented in various pleasantly coloured interactive histograms and you could search per-gene or per-disease.
However after spending a few hours, I cannot find the site again. Though I have found many sites with a great deal of data and nice visualizations.
The nearest looking site, was this one: http://plugins.biogps.org/data_chart/data_chart.cgi?id=673
But that doesn't have the level of detail that I remember.