Please help me find a web site where I can download historical (1980 -
2005) [or at least 1996-2005] data for quarterly firm characteristics
(accounting ratios) for corporations located in U.S. and/or abroad. 
The web site should charge less than $1500 for data on 24 stocks.

The following website
http://www.sec.gov/Archives/edgar/data/51143/0000950112-96-001476.txt 
provides data between for the period between 1996 and 2005.  First of
all, I would like to locate a source with the full 1980-2005 time
series.  Second of all, the data at the above website is raw data
(actual balance sheet and income statement), and I am looking for a
source which provides the data in the format that I can use as input
to my computer code - a tab delimited text file with a column for each
variable.

I am looking for historical data on firm characteristics such as (but
not limited to):  short term debt, long term debt, shareholder equity
, total assets, cash, fixed costs, gross profit, net profit after tax,
sales, cash flow to Debt ratio, ROI.  If I can't get historical data
on variables above, I would also welcome suggestions for sources of
more straight forward data, such as data on profit, sales, debt,
equity, assets, liabilities.

Thank you!

Try the Whatrton WRDS database. (if you are affiliated with a
University this would be your best bet) 
http://wrds.wharton.upenn.edu/

Otherwise, you could try S&P's compustat service.  www.compustat.com

Then again, for the amount you might be willing to pay, I am sure some
answerer on this site would be sure to get the numbers for you... even
if it means digging through EDGAR filings.