Okay, so this would be considered common sense to a lot of people, but a lot of the people I've mentioned this to had never thought of it, so I thought I share it here. So anyways, this won't bring you mountains of gold, but it will provide you with a steady cash flow for about 5 minutes of effort a day. This is a very simple trick, and very obvious, all you need to do is search the auction house for Blue items from level 65-70. Now sort them by Buyout price.
On most servers Large Prismatic Shards go for 25-40g each, so now your objective is to buyout all the blue items that will net you profit if you disenchanted them into Prismatics. Usually there will be around 5 of them on any given day. Find an enchanter to disenchant the items, and voila, profit.
Once again, I'd like to state that most people know that disenchanting BoEs can be profitable, but most people don't seem to realise how reliable and profitable this method is. Compared to say buying an item for a low price, and reselling it for a profit, this way you're guaranteed to sell, and you're also guaranteed not to have your profits eaten away by deposits after a few possibly unsuccessful auctions.
You won't bring in huge amounts gold, but it adds up after a few weeks, and it takes no effort at all, and absolutely no risk.
So in step, by step form:
1. Figure out the average price of Large Prismatic Shards on your server.
2. Perform an Auction House search for all level 65-70 Rare items.
3. Buyout all the items that cost less than the average price of Large Prismatic Shards. I usually go for at least 4g profit.
4. Get an enchanter to disenchant those items.
5. Post your new Shards
6. Congratulations, you just made a guaranteed profit.