Be sure to vote in the poll for 2012: How long are you planning on staying in Peru? One tip to remember is that speaking Spanish will help you greatly no matter how long you're planning on staying. You'll be treated differently than if you speak English all the time, it'll help you assimilate to Peru, and it'll get you cheaper prices. If you're looking to learn Spanish, check out Fluenz Spanish, Rosetta Stone, and Synergy Spanish.
The Ultimate Peru List recommends: