If I wanted something smaller I'd look at a .223, if I wanted something larger I'd look at a big case .375, if I wanted something similar, but different, I'd look at a .280 Ackely. If those don't get you fired up, perhaps your question is answered by a different type of .30/06 rather than by a different cartridge. If the rifle you currently have is a 24" sporter, maybe consider a Mannlicher stocked carbine, or maybe a gas gun like a BAR, then again its hard to get more traditional or cooler than a Ruger #1 or a Winchester 95. If the weight of your rifle has made trips afield tedious, a mountain rifle or an ultralight might be the answer.