5: BMW 525i
What is it about the 525i that has made the car so popular? Well, the BMW engineering and the fact that this generation of the car came with an optional V8 engine. To get V8 power in a sedan that small in size made for a fun driving experience and collectors are starting to realize that (via Cars Guide).
All of a sudden, this generation of the BMW has become more sought after than the previous cars, and that means the price will only rise. The 525i offered a lot of luxury for the period and continues to offer a lot of advancements. The car was fun to drive and stylish at the same time while maintaining a reasonable resale value.