Helium Properties

This is a good place to start

http://en.wikipedia.org/wiki/Helium

And here for actual lift values

http://en.wikipedia.org/wiki/Lighter_than_air

9.8 N of lift (the force to lift 1 kg) per cubic meter of gas at room temperature and sea level pressure

Regarding the lifting capacity it is simply like this:

Air weighs ~1.29 g/liter and He ~ 0.18 g/L. The difference is ~ 1.11 g/L, meaning 1 Liter of He in air lifts 1.1 gram. 1 m^3 He in air lifts 1.1 kg.

In practicality you must provide a rigid container for the above calculation to work. In case of a formless balloon you must add more He to equalize the pressure inside the balloon with the pressure of the surrounding air, which changes with altitude. When adding more He the balloon gets heavier and less can be lifted per m^3.

In case a rigid 'container' is used, you would not need any gas at all, vacuum weighs the least. Depending on the strength of the "container" you may add some light gas (He) to reduce the strength requirements. It is all a trade-off.