Metal finishes look great, regardless of if it's just on part of a model or over the entire thing. They can also be one of the most frustrating things to try to do! Here, I'll pass along some products and techniques I've used for metal finishes in the past.
Silver, aluminum, and steel paint are probably the first things people try to use. They work, somewhat. The problem with them is that they often come out looking - well, painted, not metallic. They're also a royal pain to try to brush on. However, airbrushing them gets rid of the "brushed on" look, and does help out. They also are useful on aircraft that weren't actually "bare metal," but were finished in aluminum dope or laquer.
Modellers have dealt with the problems of metal paint for a long time. One of the first thoughts that came to mind was rather ingenious... and at the same time, obvious. If you want something to look like metal... why not use metal?