When searching for used vehicles, it's difficult to put your finger on what's important. While you might have your heart set on a particular year and model, sometimes it's hard to decide if a higher resale value is a better buy or if low resale prices means you can get more vehicle for less. At under $20,000, there are a lot of options -- including many luxury nameplates that you'd never imagine you'd get a chance to drive. Here are some of our favorites.