How do I change Mirror Modifiers into Objects?

Is there a way to convert a Mirror Modifier into an actuall independent object and/or a Mesh composed of individual objects into one unified mesh?
The arms on my character consist of one arm and its Mirror Modifier on the other side. I seem to be having Weight Painting issues on the second animated arm, probably because it is seen as just a mirror modifier rather than an independent object.
A little help would be greatly appreciated!

Just click the apply button on the modifier.