my fren a D90 user and also a video buff.. was telling me about some short of video curtain problem.. basically horizontal lines seen when it goes a bit dim... anyway he mentioned 500D will hv better video, and i trusted his judgement.. but like said, its not terribly bad, probably marginally only.
actually both is similar price as i comparing it with 500D 18-200mm kit II
now I trying to find out at ISO3200, which camera is able to handle noise better and if so, how much better
actually i know what i want... GF1 is not a SLR but still a camera and I think many entry level DSLR users ard the world will hv this thought of changing to a GF1 due to size and the performance of it drawing near to a entry SLR-like performance
Still a camera what.. hehe... anyway that one is totally for the small form factor and very good video reason only... i know it can't even compete with the most entry SLR
Anyway ... I am 55% towards D90 now due to the read/seen sample of good control if ISO up to 3200 .. trying to dig up more into on 500D if it can handle as well .. then 45% towards 500D becos for almost same price, it comes with 18-200mm lens which is a focal lenght that I always wanted
if you really like the video, 500d's video is better, "less" jelly like effect compared to d90, also faster frame rate (30 fps) but the 24fps of the d90 has a more "natural cinematic feel"..i think the video will be your deciding factor as 450d is a very good camera, not that much of an upgrade in my opinion..you might want to look at d5000 also if you really like high iso performance, look at this iso review by ken rockwell, it even beat d300:
http://www.kenrockwell.com/nikon/d5000/high-iso-comparison.htm
d5000 iso performance is "a tiny bit" better than d90 due to it being a newer model, the tilting lcd's also main use in my opinion is for the video as you normally take videos at chest or waist level but take note that d5000 has no built in motor which means limited lens choices plus a whole other features missing compared to d90 like commander mode, fewer shortcut buttons, smaller screen, dedicated dial, no top lcd, etc..but d5000 has features that d90 doesn't have also like quiet mode, interval shooting, 19 additional scene modes.. here's a complete technical side by side of the three:
http://www.digitalreview.ca/content/Nikon-D5000-D90-Compared-to-Canon-Rebel-T1i-500D.shtml
so in my opinion, my ranking in order is
500d>d5000>d90 - for video
d5000>d90>500d - high iso performance
d90>d5000tie500d - for overall features
hope that makes things easy for you..
if still can't decide, ergonomics will play the biggest factor, for one 500d is the lightest of them, there has got to be one of them that your hands will feel at home the most..