About (IS) Image stabilization

[Dao]

$459.00
AF016NII700 Tamron SP AF 17-50mm f/2.8 XR DI-II LD Aspherical (IF) Standard Zoom Lens for Nikon AF-D, 6 Year USA Warranty

$409.95
2562A002 Canon EF 28-135mm f/3.5-5.6 IS USM Image Stabilized AutoFocus Wide Angle Telephoto Zoom Lens - USA

Both are new and carry USA warranty

Not much big different in price.

Note: The Tamron is not a IS (or VC in Tamron) lens. But most of the people (including me) do not feel like missing anything with the one without IS/VC

 

[zoom]

What about Sigma ?

I've found this one quite cheap. With a 18-55 kit lens and this one may be a nice combination , what do you think ?
(Guess Optical Stabilized (OS) same thing with IS.
[ame=http://www.amazon.com/Sigma-50-200mm-Stabilized-OS-Canon/dp/B002330GCY/ref=sr_1_2?ie=UTF8&s=electronics&qid=1270061566&sr=1-2]Amazon.com: Sigma 50-200mm f/4.0-5.6 DC IF SLD Optical Stabilized (OS) Lens with Hyper Sonic Motor (HSM) for Canon Digital SLR Cameras: Electronics[/ame]