What is in the center of our universe?

To imagine a "center" of our universe, we must go back to the beginning of it. Now, looking around we can see that everything in the universe is moving away from us. This means that the universe is expanding in all directions. If you were to look to any point in space, you would see all the galaxies, etc. flying away at the same rate.
Though it may seem at initial glance that WE are the center of everything, we are also "moving" (though technically, it is not actually the galaxies moving, but space itself that is stretching).

So go back to the beginning, and imagine the singularity (single point before expansion) before the Big Bang as expanding like a soap bubble. Visualize that soap bubble growing and growing. Whatever particles were in that bubble would have the space between grow larger so that they seem to be moving away, even though they are not.
Therefore, since our universe (the soap bubble in this analogy), is expanding from all directions and not from one stagnant point, there is not a true "center".