Mmm. Hardsuits, Boomers, and Moteroids (use once, then discard 
) are cool, but when it comes time to make a firm statement, Orbital Particle Beam Satellites are the way to go. Wether raining celestial-themed death on the petty insects who deny your divinity, holding whole countries for ransom, or defending earth against hotshot pilots in the YF-19, they make anything cool. And when you can make the X-Files cool, if only for an episode, you know you’ve achieved something.
It’s little cousin, the asteroid-dropping Mass Drivers (Hardwired, Babylon 5, many others) are as effective, but lack the precision, and more importantly the style.
Likewise, any type of spaghetti missile, in the Macross/Robotech tradition, is cool, too.
Mataglap nano, from Aristoi. Turns almost anything it touches into more of itself. Only to be used when you hate someone enough to kill everyone who happens to be on the same planet they’re on, though.
Further on the Hardsuit angle, how about the “Unit-G,” which allows humans to summon the Guyver bio-armor? Fast regeration, enhanced strength and speed, telepathic communication with other guyvers, a wimpy area effect sonic attack, a gravity controller that can be used to fly or form a pressure cannon, vibration blades, and a Mega-smasher. We don’t know what a mega-smasher is, but it has a nifty shimmery special effect and a goofy name, and really, what else do you need for a final attack? And it lets you make truly terrible live-action movies, too!
How about Project Black Mind, from Hardwired? Someone irritating you? Bullies kicking sand in your face? Girls kicking sand in your face? Why not overwrite their personalities with your own via com line?
Of course, for a formal occasion, perhaps a dinner party before taking out that pesky rival country, you can’t do much better than Ifurita. She accessories well, destroys citys at will, and can run for years on a few cranks from the Power Key Staff. The ancient El-Hazardians were true masters of flywheel technology . . .
Computer game-wise, I can’t think of many. Doom and later Quake had weapons called BFGs, but the Red Riot from Shogo was, in my opinion, weapon that actually felt like a BFG. And it even burned your enemies shadows into the ground! Unreal Tournament’s Redeemer is more powerful, and Slave Zero’s final weapon looked much cooler, but they didn’t have the same impact . . .
Actually, Shogo’s Shredder, the basis for Quake 3’s BFG, was pretty damn cool, too. Would have been cooler if it was ballistic, though . . .
Hijack: Actually, I thought BGC2040 was better than the original in some ways, (It was more than three times as long, after all, and a full third of BGC got cut out . . .) but tech certainly wasn’t one of them . . . They really can’t be compared directly. One’s an original short OAV series, ones a TV series using an existing property . . . And you can have endless fun shouting “I’m not Makoto!” every time Makie appears onscreen.
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“Gun! Death Blossom Mode!”