I'm interested in statistics on incomes of Americans within the
different percentile ranges. It would be good to see as much as
possible of:

- both mean and median incomes, within each of:
- lowest 1%, lowest 5%, every 10% percentile increment, top 5%, top 1%, or similar,
- if possible, broken down by wage income, investment income,
entitlement income, and/or any other "significant" source of income.

Also,
- The (estimated) total number of people in the sample (from which the
numbers within each percentile group are easily derived).
- The source of the sample, e.g. Is it working people? Working-age
people? Does it include people with no income whatsoever?
- Of course the references consulted!

Sources probably don't provide every facet of what I'm looking for, so
a "mostly" answer should be good. I'll offer a tip for degree of
completeness. Thanks!

Census Bureau 2003 data
http://www.census.gov/prod/2004pubs/p60-226.pdf

Perecentile Household Incomes (based on the 112,000 households [22,400
households per quitile] in the US)
0-20%   earned 3.4% of US income
20-40%  earned 8.7%
40-60%        14.9%
60-80%        23.4%
80-100%       49.9%

The average household earned $43,318, so doing the math that means the
average (mean) household in each quintile earned:
0-20%   $  7,364
20-40%  $ 18,843
40-60%  $ 32,272
60-80%  $ 50,682
80-100% $108,078

It's a start if nothing better comes along.  Hopefully a researcher
will know where to get the more detailed info you need.

**that should be 

"based on 112,000,000 households [ 22,400,000 households per quintile] in the US"

as opposed to 112,000 and 22,400