2 Storey house rendered inside ACA2009 and tweaked in gimp.org. Learnt some good tips on adjusting images in Pshop from a local pc magazine. How to make the sky blue (what's with Autocad's sky colour - it looks like storm weather) and how to brighten and sharpen the overall image. Really helpful in lifting a dull output.
Tweak 'Level' under 'Colors' - drag bottom and top controls up & down to remove 0 levels on chart (can't be 0 because it does change the image) and then
Boost the Hue Saturation to boost levels (particularly blues).
These images are easy to produce once you've done the hard work of modelling the building. Rendering time is a few minutes generally, this image fair bit longer with a presentation setting and the 3d trees.
I think the PN and process makes this a much longer exercise for small projects that it needs to be and I rant about this on my blog.
Cheers and thanks for the previous comments.