I use ACDsee as I find Photoshop so hard
Apart from the obvious things like light and composition you can adjust the contrast, lightness, levels, sharpness and colour saturation. I use a 30D and just shoot in jpg. You can also use exposure bracketing and WB bracketing in camera. It's worth taking a couple of shots on different white balance settings too to find out which works best in your particular environment.
My original pictures straight from camera often don't look that great but by playing around with them I get some really bright and colourful pictures.This is especially important here in Spain as the harsh light often bleaches out colour.
So, play with your camera settings, get to know them really well before you go and use PP software.