Those that have mentioned there is plugins for this, that is correct. But this is the HEART of WordPress. One of the biggest grips I hear is people get aggravated with using the WP Editor.
Some have said why do they call it a WYSIWYG Editor because very seldom is that is the case, it needs to be a WYSISWYG
Would be very nice to see this in WP 3.8 or no later than 3.9.