With the Decreasing prices on most items, I have noticed 3 things I tend to buy on the Auction house to vendor after I purchase it for profit. With a nice vendor price of 1g each, Icy Dragonscale, Jormungar Scale, and Iceweb Spider Silk are purchased quite often for this purpose. So if you prefer not to use auctioneer (due to system resources) look out for these on the auction house.
On the subject of these three things, it is pointless to list these on the Auction House for any value close to 1g each. Vendor them, save your self the time and get the quick gold.
If you do use Auctioneer, here is a quick guide on how to search for vendor items.
Using this tool helps you bid/buy many things on the auction house that you can purchase to make a profit from vendoring. I usually bid/buy 100-200 items a day for vendoring. This isn’t extremely profitable, but very easy that just takes one scan with Auctioneer.