Kovacsland is chock full of well-researched facts, and provides a good, fairly objective look at Kovacs' life and work. This provides a good balance to the other two books. The Ernie Kovacs Phile is important because it was the first book on Kovacs, and Walley brings a unique flavor often writing in the style of Ernie's unique vernacular.  He wrote me that "it's written in a uniquely Kovacsian style...how can you write about EK without having his cigar ashes drub into your typing keys, eh?".  Sing a Pretty Song was written by Edie, and was written around the same time Rico was working on her book, and so there are no quotes etc from Edie in Kovacsland, and so the two books complement each other. Reading all three provides a good all-around picture of the man. Andrew Horton's Ernie Kovacs and Early TV Comedy (published in 2010) is a nice study and overview of Kovacs' work itself.

In 1986, the Museum of Broadcasting, (later the Museum of TV & Radio and currently known as the Paley Center for Media) published a companion book in conjunction with its huge Kovacs exhibition called The Vision of Ernie Kovacs.  The book contains a TV videography, a lot of great stills as well as some well-written, loving critical essays of Ernie's work.

Ernie himself did a bit of writing that was published.  He contributed to Mad Magazine in the 1950s and a lot of his work -- like illustrated editions of his "Strangely Believe-Its" -- is reprinted in things like Mad For Keeps and other Mad anthologies.  And, of course there is the novel Ernie wrote, Zoomar. There's also the book Ernie wrote (quickly) called How to Talk at Gin.

All of the books listed here (except for Andrew Horton's) are out of print, but you should have no trouble finding them on Amazon, eBay or a book site like Alibris.