I hate sounding repetitive......aw heck, I lied.

The rudder is perhaps my most-used surface in aerobatics and 3D, some would argue I use it too much. I am not especially 'good' at flying, but I certainly got much better once I had learned to use rudder effectively. You can't hover, Knife-edge, correct for wind, line-up for landings, point-roll, do spins, harriers or flat-turns without rudder....(there's probably much more).

The plane that taught me to use rudder well was a foamie from http://www.chargerrc.com (I love these planes for 3D practice).

Learn to use your rudder effectively and you will be a better flyer than more than half of the 'experienced' people who have been 'flying' for years. Sadly, there are many, many people who never bothered to learn proper rudder control.