This is legally interesting: Nimbus Sans is a metrically compatible clone of Helvetica, released under the GPL (General Public License). You can download and use it freely, even commercially, as long as you respect the GPL terms.
Helvetica Neue LT Std is a popular sans-serif font family designed by Linotype. It's a revised and updated version of the classic Helvetica font, with a more refined and modern look. The font family consists of 18 weights, from Ultra Light to Extra Bold, making it suitable for a wide range of applications, from body text to headlines. download helvetica neue lt std font family