[ReBorn_Spirit]

Actually the closest thing we have to an "experience bar" is actually when you press Q or open the inventory. When you look in the top left corner of that, that is where the best place for a "bar" would be.

Something that would be a bar that when you held your mouse over it it would give detailed numbers instead of just a percent which would always show.

Expanding on the idea, the same should be done for all the skills you level up just below that, in the same manner. Showing details such as currentexp/requiredexp to next level. Just simply put the level number before the bar in a circle or something and it would look nice too.