The websites I know of:

www.google.com : Can often find out quite a bit about a product.

www.checkupc.com : Great claims, but never successful in finding something. I believe it's volunteer based. They claim 6 Million codes in the database.

www.froogle.com, www.amazon.com : good for shopping/price comparison

www.upcdatabase.com : very comprehensive, but not that much info.

www.upcfoodsearch.com : For food products. Not very comprehensive, but it will usually find the manufacturer..

http://upcdata.info : Interesting site..

I think the main ones to me are www.google.com, www.upcdatabase.com, and www.froogle.com


The scan app from Android uses the following:

"What is the backend?

Because scraping store APIs can be bandwidth expensive, the actual searching is handled by a separate server written in Python. The Android phone feeds the scanned UPC/ISBN code and a current zipcode to the server, which then feeds back a very condensed XML response with the essential data. Here's a list of the specific sites/APIs that we scrape:

* UPC Database
* Amazon.com API
* Half.com API
* Yahoo API
* Barnes and Noble (items and store locations)
* Hastings (items and store locations)
* Local libraries (San Francisco, San Jose, Portland)

The Python script will mark any nearby stores or libraries with an address and phone number. For metadata, the script fills in details from any available data source, which means it can still provide answers even if one or more APIs fail. "

From: http://scan.jsharkey.org/

I don't know if the author would be willing to share the Python back end or whether is is already open source.