The four elements (Earth, Air, Fire, Water)
The human body
The planet Earth (equal-armed cross inscribed in a circle)
The gods Mithras, Attis, or Tammuz (Tau cross)
Egyptian hieroglyphic for life (Tau cross surmounted by a loop)
The classical Christian cross, based on the Roman torture device and known as the Latin cross, has its lower leg longer than the others.
The equal-armed cross is a very basic shape and has been used in human culture for centuries before Christianity. Anything that can be divided into four sections can be represented by a cross, four elements, the four cardinal directions, four seasons. And that's just one association.
It's weird how the power of a cross can impinge on anybodys psyche when presented as an answer to a problem. My local soccer team were one of the few in the UK not to win a major trophy until a legend started to circulate that this was down to a gypsys curse from when the ground was being built. A manager came in and erected crucifixes on the the floodlight pylons. The club didn't win anything but the fans (beer drinking heathens to a man/woman) loved it!