I place in another Vermont Photo Place Gallery contest this week, with an image I shot with a Panasonic GF-1 in Paris last year atop Centre Pompidou. The theme for the contest was Stormy Weather; I sent in 5 cloudy shots from that day, and this is the one they picked:
The RAW image looks like this:
The final image was achieve mainly through the use of the Lightroom 3 Gradient tool. Now one of the best things about the Gradient tool, is that you can stack them; add gradient on top of gradient on end. For example, the top image contains 4 gradients, but the same image below contains 7 gradients:
Once I lay down a new gradient, I adjust the lightness/darkness, and contrast. Then I grab for a new gradient and keep tweaking. Some gradients are long and smooth, others short and break rapidly. Others yet run diagonally to darken corners like you would with a vignette, but more adjustable and asymmetrical. Sometimes I also add Clarity in a gradient to improve local sharpness.
Each Gradient is represented in your file as a small round dot which can only be seen once you click on the Gradient tool (or use the keyboard shortcut "M"). Because everything is proxy based, you can always re-edit a gradient later by clicking on any of the dots and changing the settings. Here are the above 7 in a screen capture, I've colored red them so they're easier to see: