IF YOU DON'T KNOW THE DIFFERENCE BETWEEN AN ENTRY ID AND A DISPLAY ID, YOU NEED TO GET MORE FAMILIAR WITH THE SQL STRUCTURE BEFORE READING THIS.
As of patch 3.3 Blizz implemented a dbc check to make sure the weapon is equipped correctly. This broke a lot of people's custom weapons because abilities that require melee weapons, or like backstab needs daggers, shield slam requires shields, etc. won't work. Armor & weapons can still be equipped, but you have to do it manually instead of right-clicking the item from your bag.
So to make it equip on right-click & make sure the game knows what type of weapon it is, you must use a valid entry id. Most people just replace low-level gear & steal the item ID from it. But that means you will be missing items from your DB! So you need to use an EntryID that is in the dbc's, but not in your database.
deep6ixed posted some unused weapon IDs here.
I made a complete listing that includes all items from the DBC because I am far too lazy/don't have the time to parse the unused id's. So it's up to you to find an unused Entry ID. The most accurate way of accomplishing this is to compare it with your item database. The lazy way is to check on wowhead (http://www.wowhead.com/item=XXX --- Replace XXX with the entry id) until you get one that says "This item doesn't exist or is not yet in the database." But be careful because some databases have some incorrect entry ids, and they may conflict. But if Wowhead says it doesn't exist & your db has it in there already, as something else that you didn't put there, that generally means your database sucks.
Now once you have your entry id, you can make your items however you want to make them, WoW-V is fine too, just use the unused entry id you just found, and it will equip on right-click from your bags & weapons will now work with abilities & spells correctly.
ONE NOTE: The display IDS found in my chart is only used for the icon the item has while in your bag. When buying from vendors, or after you equip the items, the icons should match the displayid you gave to them item when you created it.
Hope this helps a few people, especially those not familiar to working with the DBCs.