Compared to...

Studio scene comparison (higher sensitivities)

There's little visible (or measurable) difference between the EOS 450D and its predecessor at higher ISO settings, and both show Canon still has a slight edge over its rivals at this end of the market (thanks to superior processing and a more light-handed approach to noise reduction).

As usual Sony (and to a lesser extent Olympus) are using stronger noise reduction which has softened the output slightly and - in the case of the Alpha 350 - still failed to get rid of the strong chroma noise. Note that the EOS 450D samples below where shot with noise reduction turned off; turn it on and you get results that are essentially free of chroma noise.

ISO 800

Canon EOS 450D Nikon D60
Olympus E-420 Sony Alpha 350
 
Canon EOS 400D

ISO 1600

Canon EOS 450D Nikon D60
Olympus E-420 Sony Alpha 350
 
Canon EOS 400D