The one on top is the first ever appearance of KITTY PRYDE. The letter was sent by John Byrne to Chris Claremont.
A guy named Jonathan Mueller, whom I am now extremely jealous of obtained this awesome piece on eBay for $1625. In my mind, it's worth at least $25,000.
This letter is also responsible for the revival of the old X-Men uniforms and what came to be known as THE NEW MUTANTS.
Read Jonathan's comments on his purchase here.
The next letter is one sent by Jim Shooter to Randy Schueller.
Forever uncredited by Marvel, Randy is responsible for BLACK SUIT SPIDER-MAN which later led to the creation of VENOM!
Read the full story of Randy's experience here.
A huge "Thanks" to Randy and Jonathan for sharing their letters with the internet.
(It is my understanding that I am in compliance with the Fair Use Doctrine.)