Canon XTi vs Sony A100: Image Stablization

Maybe I should also be looking at Nikons... gah too many choices!

The in-camera stabilization is a GOOD reason to pick the Sony A100 over the Canon XTi. Canon makes stabilized lenses, but these are more expensive than non-stabilized versions, and in the long run, if you plan on buying several lenses, that will really pay off. Plus the Sony is compatible with many older but good Minolta lenses. The Canon wins out in high-ISO noise, that's a consideration. If you want to capture a lot of low-light action, you'll want either high-ISO proficiency or a fast (large aperture) lens, or both.

The Pentax K10D is another option, loaded with features, and generally very good - it also suffers a little at high ISOs, where some "banding" type noise can occur. But this camera also offers built-in stabilization, and a wide range of compatible Pentax film and digital lenses.

Then there's Nikon, namely the basic model D40 and the advanced D80, which is comparable to the XTi and the K10D. Nikon produces great ergonomics, excellent photo quality (the D80 is known to lose a little detail at ISO 1600, because it applies in-camera noise reduction, but will therefore also offer better out-of-camera grain/noise control. Although post-processing noise reduction will probably offer somewhat better results, a good noise reduction program might be costly), and great flash availability and control. Neither the D40 nor the D80 offer in-cam stabilization, it again being built into the lenses (termed 'VR' in Nikon's lens system). The D80 is about the cost of the K10D. The D40 has one major downside: no in-camera focus motor means only a limited, often expensive, selection of lenses will auto-focus. There are a few inexpensive options, especially if consumer zoom is on your agenda, and if you don't plan on a large collection of lenses, the D40 is a super choice for straight-up image quality for the cost.

There's a quick going-over of the major choices in the range. There are others, like the Olympus EVOLT E-500, also the Pentax K100D, which might be better compared to the D40, being in that price-range.

You will need a tripod. Sony IS gives you less than 3 f stop IS stabilization, whereas Canon IS lens can give about 3-4 stop assistance (the newest 70-200 mm f/4L IS has state-of-the-art 4 stop image stabilization). But if you have long exposure, then you will still likely have blurring even with IS. Canon IS lens costs about several hundred dollars more than its non-IS versions. Some of the premium Sony lenses, the G series and those made by Carl Zeiss, cost more than the Canon or Nikon equivalent lenses with IS.
The Olympus has live view LCD, which may help you see your composition and fine tune the effect you want a little bit more easily than using the viewfinder. The live view LCD let you take pictures using the LCD screen, just like how you use the PS cameras. The new E-410 and upcoming E-510 both have live view LCDs at more affordable price than the E-330.
You should talk to other people who do your kind of artistic photos, and find out what you really need.

is superior to in-camera (electronic) stabilization, and will yield a better image (photograph). Note that Nikon also uses optical stabilization.

It sounds like your preferred photography will find stabilization irrelevant. You will want the camera on a tripod for your shots. Canon will provide you with a vastly superior set of lenses, and a vastly superior upgrade path for your photography. Canon is the only vendor which offers full frame cameras.

I haven't used it. But this is a user review:
http://www.bobatkins.com/photography/reviews/fisheye.html

http://www.bobatkins.com/photography/reviews/wide-angle-lenses-2.html

If you plan for using this type of lens, probably stick with the more traditional D-SLR like Canon or Nikon which have available adaptors for this fisheye lens. I'm not sure whether it can be mounted on Sony. Olympus has a different 4/3 system and may not be compatible.

As mentioned above, image stabilization is not good enough for long exposures most of the time. You will need a sturdy tripod and a remote or shutter release cable to minimize camera movement.