well the main weapons are laser based or bullet based. a blade of some sort can't hurt. Laser's make better rapid weapons while bullets still hold out for range. Lasers work off energy, but need a lot of repairs. bullet based weaponry just end up running out of ammo if you can't make more somehow.

for the marines I'd allow some smaller explosive weapons grenades maybe a smaller rocket launcher.

Try to remember the survival aspect as well. These weapons should be slightly multi-faceted.

For example on my character's exo his blades also are hooks used for climbing and a good way to grab onto something and pull it closer like a crate or fellow exo.

Also you can have weapons on your pilot. Izic carries a shotgun, and a laser pistol (which is really a modified welder).

There are other weapon types out there of course though. Flamethrowers bit risky but doable, non-lethal weapons like tranq guns and shock weapons. Pretty much if you think of it and rationalize it I would consider it.