Hi Boo, the standard accepted/played key for "Take Five" for concert C instruments (piano, flute, etc) has always been Ebm, at least in all my jazz fakebooks, as well as everyone I've ever played this tune with. Of course, if you're playing from a Bb (tenor sax), or an Eb (alto sax) fakebook, then the written key would (of course) appear differently:
http://www.aebersold.com/jazzhandbook/39_transposition_chart.pdf

- Scott

He's right Boo Boo - All the charts I ever saw were in Eb.

...maybe because the original recording by Dave Brubeck is in Ebm too.