Personally, I've always preferred literary sci-fi weapons to the ones on TV or film.  My favorite is the 
.  Might as well get rid of the whole thing, right?
I like the personal shields that David Lynch came up with in 
Dune.  Those stayed close to my personal interpretation of the novel.  Obviously not a weapon but something I thought "gee, I'd like one of those".  
As weapons go, I'll take Leeloo from 
The Fifth Element, thanks.  Indestructable, hot, fully versed in hand-to-hand combat and the antithesis of pure evil?  Sign me up.