Most of my guns are pretty bland; unique and interesting calibers is where I have a little more fun though!
The more well know but still uncommon calibers are:
358 Win (Savage Striker)
30 Herrett (Contender)
7mm TCU (Contender)
300 Savage (Savage 99)
284 Winchester (Savage Striker)
338 Edge (Jim Borden rifle)
The more obscure and unique calibers:
6.5 Badger (thanks to Biggerhammer

)
270 RUM (Jim Borden Rifle)
338/375 Ruger (Savage Striker and rifle)
375 BME (Savage rifle)
458 Arnold (Arnold Arms Stainless Hunter built on Rem 700)
I've had some other really cool/random stuff over the years but most of them have moved on to new homes.
Andrew