The Canon Rebel T1i digital SLR is Canons latest big brother in it's Rebel lineup, and is definitely one worthy of consideration. It has to be one of the better (albeit more expensive) entry level SLR cameras on the market today. Not that it makes as much a difference as you may imagine, but the D90 SLR has a smallish (12.3MP) image sensor than the more affordable Canon Rebel t1i digital SLR (15.1MP). If one was only to consider the obvious specifications, it would be a no brainer to select the Rebel T1i 15.1MP over the Nikon D90 DX.
Unfortunately for the average bewildered consumer, that's far from the truth. There exist better image sensors (SLR 40D) that could have been used here.
Megapixels is too commonly used in selling cameras, and Olympus, Nikon and the rest of the producers know that most of all. In the case of the T1i, the sales department seems to have converted the design engineers.
If the Rebel SLR T1i wants to have a more enticing megapixel ranking, with a sensor that is sort of smaller than the D90 SLR DX image sensor, then they have to use smaller pixels, and crowd them nearer to each other on the sensor. A more correct indicator of picture quality than megapixels, is pixel density. In this case, the Nikon D90 DX comes in with much better numbers (lower is better here) of 3.3 vs 4.5 for the T1i.
There are other points to remember, when dealing with a digital camera that has too many jammed pixels. As you go looking for extra lenses, you'll discover, that more megapixels means spending more on expensive lenses. The better lens with high resolving capacities that are fashioned to work with additional megapixels, will not be the the cheaper lenses.
Wait, there's more, as I'm far from finished highlighting the problems with high pixel density. Excessive pixel density can be a detriment also to ISO, dynamic range, and diffraction. Upon further scrutiny, it would appear that our first assumption of the Canon Rebel t1i digital SLR being better bang for the buck was slightly wrong.
A respected measure of image sensors using RAW data, is supplied by Dx-O-Mark. Testing between the Canon 50D SLR (same image sensor used by the Canon Rebel T1i) versus the Nikon D90 DX, show the D90 Digital SLR to be higher performing. There's every reason to believe that upcoming T1i SLR test results will line up to the Canon 50D data.