Science fiction weapons

I'm doing some research for my third book, which involves a technologically-advanced hostile alien species (Qorall) from another galaxy looking to destroy an old enemy hiding in ours. The question is what weapons such a species might have at their disposal as they slash and burn their way through our galaxy? In my short story 'Galactic Barrier', actually a chapter from my second book, I give hints on what they are capable of, e.g. destroying whole star systems by making their suns of nova, using 'black hole mines', etc.

At the moment I'm reading the Lost Fleet by Jack Campbell and he has a pretty good array of weaponry (from 'grapeshot' to 'hell lances' and 'null fields'), and am about to start Greg Bear's Forge of God/Anvil of Stars books, but I'm wondering what other types of weapon (and counter-measures) have been conceived.

I believe time travel would be the ultimate weapon, since (as in Star Trek Voyager's 'Year of Hell') with such a weapon you could simply go back in time and erase a competitor before they got too advanced. But I'm saving that for something else...

Answers on an intergalactic postcard, please, before they arrive...

Galactic Barrier is in stories
The Eden trilogy Book one: The Eden Paradox
Book Two Eden's Trial due out November