Camera Body or Lens to buy first?

I have a Nikon D50 and a Nikkor 18-135 F4.5. Should I spend my hard earned cash on upgrading my Nikon Body or buy a nice Lens?

Added (1). I currently shoot like this:
http://s1310.beta.photobucket.com/user/theodore80/library/TZ%20Photography

Are you using your current camera intuitively?

If you can get shots like this, you may be ready for a Nikon D7000.

or this

Lenses are the core of a camera system. I spent about four years building my system when I had a Nikon D100. When I did upgrade my camera, I had five excellent lenses to use with the new camera

Lens. Get better lenses.

80% of your camera budget should be devoted to lenses. If your camera is sufficient, then a new pro grade lens (f/2.8 or faster) may provide better results.

When I look at your photos, your exposure is good, so you can handle a higher end camera. However, you may want to brush up a little on the "rule of thirds" concept. That would take your photos to the next level.

http://www.althephoto.com/concepts/composition.php

Experiment a little by taking a COPY of your photos, and applying the rule of thirds and crop them a bit, and see if they look a bit more interesting.