This is a program I got inspired to make from this thread.
Decided to use python because I'm comfortable with it, it's easy for others to use and why not. You'll need python 2.7.10 for it.
If you have python 3.4 then use Hisoka's port over here.

It uses the Toribash API to check through the market inventory of any user and outputs a text file listing all of their market inventory and the best competitive value that the items have. (Ideally after you get the output file you can then go through and update your items accordingly or maybe just enjoy looking at the potential value you have sitting around in crap you don't use)
For eg,
If a competitor has an item already on the market then your competitive best value is 1 tc below that. It also takes into account when items are out of stock or not available for tc purchase in the shop.

At the end of the output file it also gives you a figure for the total best competitive value of your market inventory is.

Possible things for the future:
-Able to specify which items to value (active/inactive/market inventory/specific set/etc)
-Change output to indicate which of those items you already have at their optimal price in the market and order the output to show the ones that are furthest above the optimal first
-Look into the market search call and try to get it working faster and more efficiently if possible
-Start more work towards making a proper Toribash API library in python so this useful information automation is accessible to more people.

FAQ about API here for more info.
Questions, help, comments, improvements feel free to post here.

Edit: