What baseball cards are worth a lot of money is better answered by a test than by a list, because the same card in two conditions belongs in two different categories and because lists go stale. The test is three questions, and a card has to pass all of them.
Is the supply small, and can you show it
Either the card states its own print run, or its sales record shows examples appearing rarely. A listing that calls a card rare is making a claim. A serial number is evidence, and so is the observable frequency with which examples come to market.
Is this copy near the top of its condition range
Among scarce cards, the steepest part of the price ladder is at the top, so the expensive examples are overwhelmingly the best-preserved ones. That is why high-grade examples of old cards carry the prices that make the news, and why an average example of the same card is a different proposition entirely.
Are people competing to buy it
High prices come from competing buyers, which requires a community that wants the card rather than one collector who does. Completed sales show you that directly: several recent sales at similar levels means competition, and a single sale after a long gap usually does not.
What to do when a card passes
Price it carefully with five comparables at your condition, consider grading if it is raw and sharp, and take your time. Cards at the top of this market reward patience and punish a fast listing, because the buyers who pay those prices are looking for the right example rather than any example.
Questions people ask about what baseball cards are worth a lot of money
Do I need to know the famous cards by name?
No. The test uses properties of the card in front of you, which is more useful than a list because it also works on cards nobody has written about.
Can a modern card be worth a lot?
Yes, and increasingly it is where the very high modern prices are: low-numbered parallels and manufacturer autographs of players in heavy demand.
Is a high grade enough on its own?
No. A perfectly graded common card is a common card with a number on it, and the fee has still been paid.
Where do the headline prices come from?
Auctions of scarce, high-grade, heavily collected cards, which is all three conditions at their maximum at once.