> Usage Note: Throughout most of its history in English myriad was used as a noun, as in a myriad of reasons. In the 1800s, it began to be used in poetry as an adjective, as in myriad dreams. Both usages in English are acceptable, as in Samuel Taylor Coleridge's "Myriad myriads of lives." This poetic, adjectival use became so well entrenched generally that many people came to consider it as the only correct use. In fact, however, both uses are acceptable today.
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!
thefreedictionary.com is only one of many dictionaries that use "myriad of" in their examples. Here are some more: http://www.yourdictionary.com/myriad
Speaking from an en_UK POV 'a myriad of' is how I'd normally use it; the poetic adjectival form is nice in poetry, but doesn't feel quite right to me in normal language.
Whether I'm correct to feel like this is left as an exercise to the reader.
When I lived in London I noticed lots of people got it wrong. If you think of it as a synonym for 'many' rather than 'lots' it's easier to slot into sentences correctly.
> Usage Note: Throughout most of its history in English myriad was used as a noun, as in a myriad of reasons. In the 1800s, it began to be used in poetry as an adjective, as in myriad dreams. Both usages in English are acceptable, as in Samuel Taylor Coleridge's "Myriad myriads of lives." This poetic, adjectival use became so well entrenched generally that many people came to consider it as the only correct use. In fact, however, both uses are acceptable today.