Defenses against 51% attack?

Currently, the only defense against a 51% attack is that it's costly. I imagine that making it more costly would be more beneficial -- so I'm wondering if an algorithm can make that happen. For example, what if miners established reputations as "credible" miners -- so if an army of brand-new miners came on-line they would be shunned by the network? This way rogue machines would have to sustain their attack making it more costly?