Katana forged by Masamune
Considered to be the greatest Japanese swordsmith ever, Masamune created blades that were thought to generated peace and calm within the bearer. The Honjo Masamune was handed down from Shogun to Shogun ever since the Tokugawa shogunate.
Katana forged by Muramasa
Possibly the second greatest, Muramasa's blades are said to induce bloodlust in its wielders. He is said to be a student of Masamune's though the dates they likely operated in precludes their ever meeting.
Still, this created a good legend.
Muramasa once challenged Masamune to a contest to see who could forge the greatest weapon. Once the forging was done, to test the weapons, they thrust them into a stream, blade facing into the current. Muramasa's blade cut everything in its path. Fish, insects, leaves, even the air was sliced by the sword. Masamune was impressed with his student's work. He thrust his sword into the stream. Fish swam right up to the edge, then moved around it without touching the blade. Leaves, insects, even the water and air flowed
around the blade rather than touch it.
Muramasa mocked his master's skill. Meanwhile, a monk who had watched the test approached and offered his opinion.
"The first of the swords was by all accounts a fine sword, however it is a blood thirsty, evil blade as it doesn't discriminate as to who or what it will cut. It may just as well be cutting down butterflies as severing heads. The second was by far the finer of the two, as it doesn't needlessly cut that which is innocent and undeserving."
The above is the most popular version of the story. It's in a couple of different books that I have read. Check out
http://en.wikipedia.org/wiki/Masamune
for a slight variation on that story, as well as several larger variations, and more info on Masamune and Muramasa