VendorMate will help you handle your vendoring transactions.
VendorMate uses filters to sort your items (currently just your normal backpack+4), each filter has a set of rules for items to match.
Filters follow a priority starting in the upper left of the gridview and going L-R and T-B.
You can set filter 1 to all blue armor, then filter 2 to any blue and it'll sort all your blue armor items into filter 1 even though filter 2 is any blue item, filter 1 takes priority.
Each filter can be sold, or you can vendor all filters, it's always worth checking the list of items before mass vendoring.
Below the filters you'll some data about what is currently filtered and its total gold value.
VendorMate also includes profiles, this means you can create profiles to use for certain in game activities where you might acquire a lot of items which have no use/value (old expansion items for example).