I like the heavy blasters in "Knights of the old Republic". They are pistols, but have what looks like a rifle magazine sticking down. I would love to see something like that in real life, pistols that fire full sized rifle ammo. :p

http://www.iamanangelchaser.com/file...ar15pistol.jpg

http://www.impactguns.com/store/medi...tol-Beauty.jpg

I guess someone really doesn't search on the internet much. The thing about imagination with firearms is that if you've thought up something new and practical...odds are someone already has done it

The space cowboy
 

Han solo DL-44 BLASTER

The shrink gun from Duke Nukem

http://www.youtube.com/watch?v=HW_9SGrc4Oo

The M41A Pulse Rifle from Aliens,and maybe it does not qualify as a firearm,but having a Zat gun from Stargate SG1 would be nice too.

I guess I should have tweaked my Google search.
But I still like the shape of the Heavy Blaster.

I'm surprised no one mentioned the Zorg pod from the Fifth Element yet.