This TEDx talk about coffee claims that coffee is the #1 source of anti-oxidants in the US diet.
Is this true?
According to Dr Joe Vinson, yes, or at least it was in 2005. I can't find an online text of the study, but it's reported/recapped in many places. I haven't seen a newer study that directly measures antioxidants in the US diet.
Dr Vinson measured in milligrams the top 10 sources of antioxidants consumed on average in the US diet. Coffee was far and away the number one source at 1,299 mg per day. Black tea, the second source, was not even close at 294 mg per day.
However, that's the amount consumed, not necessarily absorbed by the body:
Dr Vinson's study was an in vitro test, and he emphasized in an American Chemical Society news briefing that there are limitations to this kind of study, including not knowing how much of the antioxidant compounds are actually being absorbed by the body.
Still, unless the absorption rate is vastly different for coffee/tea/fruit/etc, coffee should still come out on top. After coffee and tea, the next highest was bananas at only 76 mg.
Here is one 2004 study about antioxidants intake in Norwegian adults, because I believe the question is more about coffee than the United States, right?: "The intake of coffee contributed approximately 11.1 mmol, followed by fruits (1.8 mmol), tea (1.4 mmol), wine (0.8 mmol), cereals (i.e., all grain containing foods; 0.8 mmol), and vegetables (0.4 mmol)...Surprisingly, the single greatest contributor to the total antioxidant intake was coffee." Source: PubMed
Here is a search result for "antioxidants" in Cochrane Summaries. Conclusions of all 30 or so studies related to antioxidants are that there is insufficient evidence about their effectiveness.