I don't know what state the development of alien weaponry is at but I had a suggestion (should you be looking for more variety) for an alien weapon.
Basically it would be modelled around the concept of a burst fire machine gun. However, instead of firing three separate projectiles, it streams a beam (the equivalent length of three laser bursts) towards the same point. Obviously this would be a heavy weapon which if on target would be deadly but would lack the spread fire of an actual burst fire weapon.
I presume that you already have an alien equivalent of the machine gun, but obviously a beam gun would be uber cool.
I don't know what the practicality of such a weapon would be like but I just thought I'd put it out there all the same. It would be nice if the alien weapons weren't just masked equivalents of the Xenonaught weaponry.