I am not sure if it is a general consensus, but I found default colors produced from the two Canons I owned (XSi and 50d) lacking the punch that I desire. I actually also owned a Nikon D90 briefly just because I liked the vivid colors it produces (in fact Nikons are known for that.. isnt it?). Here is an example:
Unfortunately I had to return the Nikon because of sensor problems, and ineffective live view.
So now, I am a happy camper with a Canon 50d, and while looking for a way to give its default colors a punch, I came across the ability of Canon's Picture Style Editor to allow to remap the colors (upto 100) in the HSL space (Hue, Saturation, Lightness). Note that a simple boost in saturation and contrast settings didnt do what I wanted. This is because the colors come out differently treated by default (in RAW format) by 50D and D90's sensors.
Here is a first attempt at vividifying the picture styles, for landscape. The vividified image is the second one:
Here are 100% crops from the images before/after the picture style application:
And here is the same location with a Nikon D90 (on a different day though, so not directly comparable with Canon shots):
If you like the work, please drop a comment here. Thanks!
Updated 02/20/2010. I get many emails every week asking for my custom picture styles, and how to upload them to your camera. Here are the answers:
 If you are interested in a copy of the picture styles that you can import to your Canon 50d camera, visit this link, and download the files. No catch here, its available for free. I am a big proponent of the "free resources for all" policy:-)
 Check this link for how to upload a custom picture style to your Canon camera, provided your model supports it. If it doesnt support it, you can still apply picture styles after you download pictures to your computer.