The most recent addition to the Hall of Fame case in my office is this pair of 1920s cleats worn by Joe Sewell (1977 HOF inductee).
Along with the cleats I also received a letter from Joe Sewell written to the previous owner as well as a gold HOF plaque postcard and the original box addressed by Mr. Sewell to the previous owner (which is who I bought them from).
Joe Sewell was the most difficult man in major league history to strike out. In 7,132 at-bats he struck out only 114 times. He also holds the record for consecutive games without a strikeout, at 115.
http://baseballhall.org/hof/sewell-joe