Hollywood memery of the USSR aside.
There is no single standard for the Imperial Army. There are several models of approximate standardization issued to the various billions upon billions of Imperial Army soldiers about the Galaxy. Generally due to shields and risk of feed back they're ballistic or energy weapons which fire a bolt rather than a continuous laser (basically pulse rather than laser).
The Imperial Guard is a bit more standardized (though they're much smaller than the Imperial Army) between a few ballistic, pulse, and gravity based weaponry.
Imperial Marines generally carry similar equipment to the Army except practically everything is tailored for void operations, short term expeditionary forces, orbital drop assaults, or planetoids with little to no atmosphere.