Some nasty things have been said about Gradient Analytics, even resulting an SEC investigation of the firm that was dropped in short order.

But as Herb Greenberg points out in his latest column (subscription required), the research firm has about as stellar a track record as you will find, having been among the first to raise questions about accounting at Krispy Kreme Doughuts (NASDAQ: KKD), Children's Place (NASDAQ: PLCE), and Biovail (NYSE: BVF).

Now, in a report available free on the firm's website (a must-read if you are even thinking about buying financials), Gradient wonders about the accounting at Washington Mutual (NYSE: WM), Citigroup (NYSE: C), Wachovia (NYSE: WB), Wells Fargo (NYSE: WFC) and, my personal (least) favorite, Countrywide Financial (NYSE: CFC).

According to Gradient's report, the financial statements of these firms raise serious questions with respect losses being hidden on assets that are being held to maturity (essentially failing to take appropriate writedowns), shifting loans into "assets held for maturity" to avoid taking writedowns, the use of "not necessarily fair market values," off-balance sheet arrangements, and the concealing of the "after-effects of aggressive gain-on-sale accounting."

Herb Greenberg's Weekend Investor column focuses on the need for investors to be more skeptical or, as he calls it, detective-like. By looking deeper into the numbers than just the earnings per share or revenue growth, you can sometimes uncover signs of trouble before most Wall Street analysts do. And with increased disclosures as a result of the Sarbanes-Oxley Act, there may be more red flags to be found than ever.

Unfortunately, I suspect very few investors have the skills to read a 10-K or 10-Q critically. Most of us just take everything at face value. But, learning a little bit of "forensic accounting" is a lot of fun (you really do feel like a detective) and may help you notice some danger signs. Here are my favorite books for digging deeper into financial statements and seeking out signs of fraud or misrepresentation:

Financial Shenanigans: How to Detect Accounting Gimmicks & Fraud in Financial Reports by Howard Schilit. Probably the best book on accounting fraud.

Quality of Earnings by Thorton O'Glove. I found this one dry and boring, but it's written by one of the first experts in the field, and contains some great examples.

The Art of Short Selling by Kathryn F. Staley. While not exclusively about accounting fraud, this contains some interesting stories of companies that were engaging in creative accounting. And, if you become an expert on creative accounting, short-selling may be a way to a profit from it.