I've advocated this before. Some people think it's too much effort, but it makes sense. It's a method I borrowed from my previous employer.

Your schematic can be your project "master." To do this, your schematic/PCB library has to have a lot more useful information than simply a generic part number and a footprint.

Most EDA tools allow you to add user fields to the libraries. So, create a user field called VENDOR and another called VENDOR_PN. (Maybe even do a DIGIKEY_PN.) Create a library "component" (or whatever your tools call it) that includes vendor name, vendor P/N, etc. so when you place that component on your schematic, everything's there. Most real schematic tools allow you to export a BOM and those fields will show up on the BOM.

Now, to make this the most useful, you'll need to have individual components in your library for each resistor value. Yep, my library has a hundred or so different resistors, capacitors and what-not. I find that it's a lot easier to get the right info up front than to have some post-processing that finds the right part number for that resistor you put at R120.

To go further: you can create a database (Access, MySql, Filemaker, pick one) that uses the same name you give to a component in your library as the main index. You can add fields like # on hand, price, even alternate vendors and part numbers. It just depends on how complex you wish to make things.

Good luck!
-a