Pastor Romanuik from Ivano-Frankivsk will get a kick out of this post because he knows how much I loved the symbolism of the Eastern Orthodox cross after he explained it to me.
The Eastern Cross, recognizable as the cross used by most Eastern and Russian Orthodox Church's, is distinctive in form from other crosses used by Christian's. This, also being on of the most distinct images of the Orthodox Faith, is the three-barred cross that rests high upon the onion domes of Eastern European cathedrals and is sold as an icon's at the churches themselves. It is a distinctly recognizable design with its slanted lower third bar and top horizontal bar built on the foundation of the Latin Cross.
The standard Latin Cross, with its vertical bar crossed two-thirds of the way to the top by a single horizontal beam is, in its most basic form, representative of the cross used in the crucifixion of Jesus. For this reason the symbolism of the cross is both sorrowful and supremely beautiful as it portrays Jesus perfect sacrifice for our salvation. The Eastern Orthodox Cross builds on this with the topmost bar which lies directly above the bar to which Christs arms were affixed.
The tradition of adding the shorter horizontal beam to the upper region of the cross is not widely debated as is the meaning of its slanted lower counterpart. This topmost bar is representative of the plaque bearing Pontius Pilates inscription written in Latin, Greek, and Hebrew, "Jesus the Nazorean, King of the Jews" (Luke 23:38). The letters INRI typically placed on this beam are derived from the Latin which reads, "Iesus Nazarenus Rex Iudaeorum".
There are many varied accounts concerning the meaning and origin of the slanted lower bar present on the Orthodox Cross. In early forms from Byzantium, this lower bar appeared perpendicular to the vertical bar. This is believed to have been a representation of the footstool that may or may not have been present on the cross of Jesus crucifixion and onto which Christs feet were nailed. There are many possible interpretations and inferences as to the origin of the slanted bar in the cross. Among all the theories, the oldest and most common symbolism is from an eleventh century tradition. This tradition is also the reason for my excitement, which you may or may not share.
Legend holds that the slant symbolizes a scale of balance. The thief crucified to Jesus right found salvation at the end of his life and would ascend to heaven, while the thief on the left, who rejects Jesus, would descend downwards to hell (Luke 23:39-43). Thus in this interpretation, Christ and the Cross isn't simply a symbol of a sacrifice, but also a balance of justice. While the traditional Latin Cross portrays the price Jesus paid for each and everyone of our sins, the addition of the slanted bar conveys the consequence, the resulting possible redemption because of Jesus crucifixion. It completes the story.
A tad bit of history that I uncovered in my research, which probably interests you even less then what you have read up until now, is The Cross of St. Constantine, which resides within the monastery of Vatopedi on Mt. Athos in Greece. This seemingly insignificant cross is of the three-barred barred variety. It was hidden during the tenth century from Arab invaders and said by legend to be that of the monastery's original founder which predates the adoption of St. Andrew as the patron saint of Russia. If this is the case, then the origin of the slant in the Eastern Cross is not of Russian descent, but is instead Greek. Scandalous!