by Patricia Sellers

It’s an important next couple of days for JPMorgan Chase .

The company reports earnings tomorrow morning.

And on Thursday morning, we’ll see how far the $100 billion bank–yes, that’s how big, in terms of annual revenues, JPMorgan has grown through the financial crisis–has surged up the Fortune 500.

I know. But I can’t tell you. Watch for the Fortune 500’s release at 7:30 a.m. Thursday.

So, it’s a good moment to share a few thoughts about CEO Jamie Dimon’s letter to shareholders. It is, except for one other–Warren Buffett’s letter to shareholders of Berkshire Hathaway –the best annual report letter out there, in my view.

“Painful and a lot of work” is how Dimon, who writes his letter himself (with a dose of editing help) describes the process. I’ve heard him cite Buffett’s “unbelievable clarity of thinking” as one of his inspirations.

This year’s letter has gotten kudos for Dimon’s candor and clarity about the business. (Even as profits doubled to $12 billion last year, he brands JPMorgan’s results “mediocre.”) Meanwhile, his section on “Developing Leaders” says plenty about his own aggressive personality. “(In a cold-blooded, honest way, leaders emphasize the negatives at management meetings and focus on what can be improved…”)

But the thing that has stuck with me since I read this year’s letter a couple of weeks ago–and pops to mind at every meeting I’m in lately–is this, about the importance of full disclosure inside your own company:

“Anyone in a meeting should feel free to speak his or her mind without fear of offending anyone else. I once heard someone describe the importance of having ‘at least one truth-teller at the table.’ Well, if there is just one truth-teller at the table you’re in trouble–everyone should be a truth-teller.”

I agree, wholeheartedly. He makes a related point that teamwork–which my colleague Shawn Tully wrote about in “Jamie Dimon’s Swat Team”–requires that every teammate can be his own man (or woman). “While teamwork is important and often code for getting along, equally important is an individual’s ability to have the courage to stand alone and do the right thing.”

Besides Dimon’s and Buffett’s correspondences, what other shareholder letter is worth our rare spare time? My colleague Carol Loomis, who has been at Fortune and scouring annual report letters for 56 years(!), names one more: M&T Bank , which Fortune profiled last year in “Banking the Buffalo Way.”