Scalable Vector Graphics (SVG) is an XML-based vector image format for two-dimensional graphics with support for interactivity and animation.
You can find most of the corporate companies using SVG format to display their logo. SVG is scalable, that means you dont have to worry about image size anymore.
SVG files are relatively small in size. You still can optimize and reduce the file size by using optimizer. One of the good optimizer I use is http://petercollingridge.appspot.com/svg-optimiser.
Checkout snap SVG: https://github.com/adobe-webplatform/Snap.svg
You can generate SVG files from Adobe Illustrator, Inkscape or other image editors. I used Adobe Illustrator and ‘Save As’ SVG format to convert my logo into SVG format.