If you are buying a dSLR, then you are not just buying a camera, you are buying into a system. So you need to consider what you will be doing with it.
Canon and Nikon are market leaders and have an enormous lens and accessory list, but do you need all this? All the other systems have enough gear and accessories for the keen amateur
Although Canon and Nikon are in vogue, they do little which any of the other big names can't do. IMO, the only need to buy into Canon or Nikon is to access the huge range of lenses and accessories. If you will only be using a single or just two kit lenses, then there may be better cameras for your purpose.
Any dSLR is going to do general photography well, so it comes down to price and features.
Some have in-body image stabilisation so every lens will be stabilised, others will have the stabilisation in the lens, so you have to buy these lenses to get the stabilisation.
Some have 'live view' which allows the screen to display the viewfinder image (like most compact cameras), others do not and you must use the viewfinder. The Olympus E3 and Panasonic LC10 have fold out screens - great for overhead or low-level pictures
Many bodys are really heavy - more so with a lens. The Olympus e410 is the smallest and lightest body around (half the weight of many others)
And don't get caught up in all the pedantry about sensor size, sensor type, image noise etc, and 'poor' lenses. A 3mp sensor and a good modern lens is more than enough for 90% of all photography - so all todays dSLR's will be fine. Same for lenses, there are some better than others, but kit lenses still produce acceptable images
