Silver Age Comics (1955 - 1971)

Amazing Fantasy #15

1st appearance of Spider-Man. While this issue might not have the rarity of Action Comics #1 and Detective Comics #27, it features the 1st appearance of a very important character, which makes it very valuable. The book can fetch anywhere from $10k to over a million dollars. The large gap comes down to condition. The highest grades copies can fetch over a million dollars, while low grades usually sell for about $10-15k. 

Incredible Hulk #1

1st appearance of the Incredible Hulk. The book is very hard to find in high grade and features a high demand. It can sell from $8k to $500k depending on condition.