Does anyone have any suggestions on the easiest way to file invoices that are received? I'm working for a small single owner business with absolutely no filing system. I have started just filing the invoices (after they are paid) by the expense (materials, supplies). The problem that I'm running into is, if I'm looking for a specific invoice I need to look through the entire file and it's taking way too long. We have way too many vendors to set up a file for each one. Any input would be greatly appreciated.

That is the beauty of a good filing system, a file for each one. You can't keep track of it any other way. Doing it by materials/supplies is not the way to it, you would have to cross reference everything.

File by company name then by materials and supplies according to what you purchased from them.

I suggest you to use the free online accounting software, Numia (http://numia.biz). It provides an easy way to keep users accounts information online with reliable and secured data transfer. With easy forms for invoicing, purchase and bank reconciliation it is easy to maintain accounts. Try this software!