"Gamer's Edition" Guinness World Records book, the Mega Man series was certified with the record of "Most Number of Games in a Single Series." That's not too hard to believe -- there were about a million Mega Man games in the main series and various spinoff series before the DS, and the DS games have been coming in multiples.
What's most amusing about this record is that, according to Capcom's blog, Guinness arrived at it without even considering all the Mega Man games -- basically, they failed to arrive at a full count, and Mega Man still beat other series. They didn't just forget Japan-only releases like Wily & Right no Rockboard, either -- Mega Man Soccer failed to make the list, and that was a U.S.-released game starring the original Blue Bomber. No doubt it omits Hi-Tech Expressions' Mega Man and Mega Man III as well.