Came across this cool (but hardly complete) list of services aimed at consumers from Amazon.com web services.

http://solutions.amazonwebservices.com/connect/kbcategory.jspa?categoryID=75

Three that I'm trying out are

1) Techno Tracker
http://solutions.amazonwebservices.com/connect/entry.jspa?externalID=349&categoryID=75
"A Flash tool that creates a dynamic graph of the top 100 selling Amazon items in a particular field, so the user can deduce the best value product."

2) TicTap
http://www.tictap.com/
Specifically, searching Amazon by mobile and SMS

3) I Feel So Used
http://www.biancolo.com/used/l
Great name. Tool for tracking used item prices (books, dvd's etc) on Amazon.com.

Btw, the catalog also offers apps aimed at other user groups including Developers, Amazon Associates, and others.
http://solutions.amazonwebservices.com/connect/index.jspa