I knew nothing about the Stanley Cup before I did a lot of Googling, but I'm now convinced it is the best trophy among the professional American sports.
Let's start with a lightning round: It's made mostly of silver, it's been at the bottom of a couple pools and at least one river, it was allegedly a chalice for a player's urine, a couple babies have been baptized in it (probably not in the aforementioned urine,) it's been to war and you can make it out of Rice Krispie Treats.
The cup was named after some guy named Stanley who was one of the first important dudes to get jazzed about hockey. He was so jazzed he started a tournament and gave the best team this $50 cup he purchased in London. I think that's neat.
The other major championship trophies in North American sports are all reproduced each year, so they are automatically less-cool. The Stanley Cup is the only one that gets passed from team to team, unlike the Lombardi, Commissioner's and Larry O'Brien trophies.
You only get the Stanley Cup for the year following your victory, and then it is vacated from your trophy case and is onto the next coolest team.
But trophy cases are not a usual resting place for the Stanley Cup. The best tradition surrounding the Cup, is the personal day each player on the championship team gets with the thing. In other sports, nobody really cares what you do with your championship ring. Unless you're the bald-headed pawn shop owner and History Channel star Rick Harrison.
But the Cup, the Cup gets released to each player of the winning team for a day wherein they are free to do as they please. This has led to some of the antics mentioned above, but also includes a Stanley Cup-centric gentlemen's' club routine and a flower pot makeover full of motherly good-intent. The Cup has been dented, scratched, and literally kicked around, which only adds to its allure.
Some of the stories are good enough that the Keepers of the Cup have started a journal following the celebration antics of the Cup.
Since I am now a huge Leafs fan, I would like to point out that the original trophy, the namesake cup, was last owned by the Toronto Maple Leafs in 1962 before a replacement had to be made.