Phyresis – Mirrodin Besieged common. Note the word "compleat" in the flavor text for Phyresis. This is not a typo for "complete." Not only is "compleat" a real, albeit archaic, word, it has a specific meaning for the Phyrexians. As Doug Beyer explained in a recent Savor the Flavor article, it refers to the state of being "perfected" by the Phyrexians.
Revelation – Chronicles rare. Revelation is a World Enchantment (which was originally called an "Enchant World"), a special kind of permanent that works kind of like Planechase. See this Arcana for the full scoop on how World Enchantments work.
Lightning Dragon – Urza's Saga rare. The first set to have premium foils randomly inserted in booster packs was Urza's Legacy. But in the previous set, Lightning Dragon was the Prerelease Card, and it was the very first Magic card to get the premium foil treatment.
Omega Myr – Mirrodin common. Alpha Myr is a 2/1 and Omega Myr is a 1/2. Sadly, even if Beta Myr through Psi Myr existed, Magic wouldn't have the numbers required to represent their powers and toughnesses.
Galvanic Key – Mirrodin common. Galvanic Key is a reworking of Voltaic Key, except that it references Luigi Galvani rather than Alessandro Volta. Or they might just both be using terms related to electricity, rather than 18th-century Italian physicists. That seems more likely.
Dwarven Warriors – Fifth Edition common. The original concept of Dwarven Warriors was that they'd be Dwarven Miners, who dig a tunnel to allow a small creature past the enemy lines. But the art showed armor that was a bit too impressive to belong to common miners, so they got promoted.
Urza's Bauble – Ice Age uncommon. The original flavor text for Urza's Bauble read, "This margin will not permit a description of the ingenious bauble." But it turned out to be too accurate: it wouldn't fit on the card.
Soulshriek – Mirage common. Soulshriek was originally named "Damien's Cry," a reference to Bill Rose's howling cat.
Animate Artifact – Masters Edition IV uncommon. Originally, Animate Artifact could affect artifacts that were already creatures, but when it was printed in Revised, it got the sentence "Has no effect on artifact creatures" added to its rules text.
Sword of Kaldra – Mirrodin rare. Speaking of Living Weapons, how about a sword that can eventually generate something to carry it? It requires Shield of Kaldra and Helm of Kaldra to work, but to be fair, Kaldra is a bit more impressive than a 0/0 Germ.
Virulent Wound – Mirrodin Besieged common. In the art for Virulent Wound, the goblin (named "Gerkk," apparently) shows his infection in the form of the huge boils that cover his back. And he's trying to get back home, which, of course, will only spread the disease.
Skinrender – Scars of Mirrodin uncommon. Note that it's called "Skinrender," not "Skinrenderer." It rends skin, rather than rendering it.
Juggernaut – Masters Edition IV uncommon. When Extended was first created, Juggernaut was banned, due to its alleged unstoppability when combined with Invisibility. That was a different time.