From the article at SearchEngineWatch:

Here’s a roundup of the mobile search interfaces for some of the web’s most popular shopping sites. The boldfaced links navigate to each service’s primary web interface. The other links offer mobile access via web-enabled phone or other handheld device, typically with slimmed-down interfaces designed for smaller displays.

Amazon.com

Mobile interface at: http://www.amazon.com/gp/aw/h.html or
http://www.amazon.com/access.

More Amazon:

Become.com

The main url http://www.become.com does a nice job of detecting browsers from mobile devices, so there’s no special URL for mobile access.

eBay

Mobile interface at: http://wap2.bonfiremedia.com/

Froogle

Mobile interface at: http://wml.froogle.com or via SMS
http://www.google.com/mobile/sms/index.html.

Frucall

Frucall is a new free service that brings you Internet shopping when you are in a store or on the street. Frucall does not need any software downloads to your phone, or SMS data plans. I covered Frucall briefly in a ResourceShelf mention, and ComparisonEngines.com ran an interview with Frucall’s CEO.

PriceGrabber

Mobile interface at: http://www.atpgw.com/

Smarter.com

Mobile interface at: Details here.

XP Bargains

PDA Interface: http://www.xpbargains.com/pda.php
WAP Interface: http://www.xpbargains.com/wap.php

Yahoo Shopping (Beta)

Mobile interface at: http://us.wap.yahoo.com/p/shopping; more info about the new service here.

And, a few lesser known mobile shopping search services: