There's so many, not sure where I'd start but on the extreme side, probably a Anzio 20mm Bolt gun.
On the more normal side, I've always wanted to have a 6.5x55 Swede Ack. Imp. built. Figure if they are still chambering the 6.5x55 Swede in modern day rifles after it's more than a 100 years old, must be something pretty good about it.
Also, I've got a bit of a crush on the necked down 6x47 Lapua.
Sheesh, I go from about the biggest, to one of the oldest, to one of the newest. lol