[superplussed]

Of course both are acceptable, why is this an audacious claim?

[Jedd]

Because it invites (not begs) the question 'to whom are they both acceptable?'.

People that contribute to thefreedictionary.com, evidently.

[randallsquared]

And people who contribute to the OED, in both the 1989 and 2003 editions, evidently.

http://www.oed.com/view/Entry/124538

http://www.oed.com/oed2/00154839;jsessionid=AC4DB817EFBADA5F...

I have had similar experiences, though, where I was convinced that some word or phrase usage was just incorrect, and where it turned out that I had just not happened across it. Fortunately, a minute of research can today fix any such misconceptions!

[kapep]

thefreedictionary.com is only one of many dictionaries that use "myriad of" in their examples. Here are some more: http://www.yourdictionary.com/myriad

A quick Google Ngram search supports the claims from thefreedictionary, that "a myriad" or "myriads" was used first and that "myriad" as an adjective was only used later: https://books.google.com/ngrams/graph?content=%28myriad_NOUN...

It looks like "myriad of" has been correct in the past and is still used widely.