Helvetica  Suggested by wafaindafont 

well, it looks so much similar to the Helvetica family to me...

or you can find some answers regarding Helvetice substitute fonts on:
http://www.dafont.com/forum/read/8596/a-helvetica-substitute

"The best substitute for Helvetica is Arial (this two font are very close)..."

you can find some family of Helvetica free for download if you don't have it already downloaded in your system.