UPS
Shipping Calculator - Calculate time and cost to any destination in the world
Tracking Tool - Enter the UPS tracking number to find out where your packages are.

US Postal Service
Rate Calculator - Find out what it costs to ship an item. International calculator also available.
Track & Confirm - Find out where your packages are by the label number.
Shipping Labels - Create an online label for shipping a package.

Auction Link - Automatically links to all of your current eBay auctions.

Auction Mapper - A cool eBay search tool that uses a power search filter.  It will even display your search result items on a map!

Auction Sleuth - Handy tools for online auctions for major auction sites including eBay Motors and Yahoo auctions.

Auction Sniper - Free auction sniping tool.  Automatically enters your bid at a specified time.

Auction Typos - A free tool that finds eBay sellers' misspelled descriptions. These items are missed when searching using the correct spelling, so these items usually have low or no bids at all.

eBay Fees calculator - Find out what your eBay fees are before submitting your item (insertion fees + extra options if chosen + final value fee).

Free Image Hosting - Easy uploading from your PC.  Allows hot linking and no login required.

Tiny URL - Tired of the long eBay URLs when emailing them to someone?  Make them tiny, Free.