I would like to see a super advanced weapon from 1000 years in the future. Something like a black hole spewing launcher that fires 1 shot per 100 MF cells....

Wait do you mean unique items that you just came across?
Such as Lincoln's Top Hat? Or his Repeater?

Or by Firelance-type do you mean redonkulously rare to find?

Cause if you mean very rare and hard to find, then yeahh, that could be good to see.
Although nothing Alien please, I think I've had a bit of an Alien-Overkill with MZ.

Perhaps something Nikola Tesla-esque?
Or some Mad Scientists ideas/ schematic.

Edit: Plus not too powerful, just something unique.

How about this. You come across a random encounter that is just a dried up husk of a corps. If you loot the corps you find 3 items.
1) A sealed envelope. If you use it you open it and read the message. It is one person asking another about the punch line for a joke, identified by its opening line. And the reply for the 2nd person with the punch line.
2) Some energy cells.
3) And a sonic pulse pistol. It’s loud, has a knockdown effect on critical hits, and does slightly less damage then laser pistol. Except on mirelurks, witch it kills outright.

Voted Yes, No and Something New.

By "firelance-unique", do you mean like some sort of unique alien weapon, or a weapon that appears only as a part of a random event, like falling out of the sky?

I hope it isn't a random event. I never found it in FO3 :sadvaultboy:

Sure, a unique random encounter weapon? I'd like it. Maybe find a dead guy that spawns randomly or whatever.

GUYS: Does not need to be alien or drop from the sky. Just a unique, random encounter only weapon.

well there's also this in fallout 3

The Wanderer's leather armor
http://fallout.wikia.com/wiki/Wanderer%27s_Leather_Armor

I have mixed feelings regarding weapons unique to random encounters since you can possibly never even see it or miss it outright (like I did the first couple times the firelance popped up, but random disorienting explosions do that.)