So it's the end of an expansion and you're dying to make a quick buck on the current mats before they become obsolete when the next expansion releases. Do not fear, because I have a great method for gold making. First off, one can always play the auction house and quickly buy out under cut items and resell at a higher value to make small margin profits here and there. Say playing the auction house isn't your game, well maybe you can look into professions.

If you currently do not have any professions or if you only have professions for personal usage, you should strongly consider utilizing your professions for a profit opportunity. Whether you spend hours in the terrain farming raw materials or if you just buy out the auction house and craft like a maniac, there is LOTS of money to be made, even at the end of an expansion.

Guilds and players are always upgrading their equipment and so enchants and gems and gear is always needed regardless of who you are and how far you've progressed. Another thing to remember is that players LOVE leveling alts and alts need STUFF! 

Current materials are usually easiest to acquire because you're generally in the current areas and the majority of players are purchasing items within the current expansion content. However, as mentioned before, players level alts or sometimes they change professions or level new professions and a demand for older mats is needed. Find your favorite low level areas and farm low level mats and sell them. They may not sell instantly but they usually sell just fine because a huge player base despises farming and would rather just buy from the auction house to progress faster. That's where you come in and solve their problems. 

I would also advise considering multiple professions amongst your alt characters. Having every profession whether you're just benefiting for yourself, your guild or the server population is never a bad thing. Ever. Here is how I prove to you that having several professions of a variety is greatly beneficial.

My druid: jewelcrafting and leatherworking.
My alt druid: alchemy and herbalism.
My mage: mining and tailoring.
My shadow priest: herbalism and inscription.
My hunter: skinning and enchanting.

I have a variety of high level alts with several different professions.
I can farm leather on my hunter and use my druid to turn the leather into gear.
If the gear doesn't sell well, I can send it back to my hunter and he can disenchant the gear and make enchants.
Or if the leather as a raw material sells better, then I can just sell the leather as is.

On my mage I can farm ore and either sell the ore as is or I can send it over to my druid to cut into gems. From there I can take basic gems and cut them into gems with specific stats or sell the gems raw as is. If certain gems don't really sell well then I turn them into rings and necklaces and I send them to my hunter to disenchant. From there he can make enchants or sell the enchanting materials as is.

There are a lot of examples of utilizing various professions to make a profit. Which one should you do? Well, it depends on what professions you currently have. If there is a shortage of materials for certain professions, perhaps level that profession or use that profession more frequently to gain an advantage on the market. If you're like me and you have almost all of the professions,  then frequently check the auction house to see what is currently selling well and what the auction house is low on. Farm those items/materials and then you can make a quick buck.

It's currently the end of Mists of Pandaria and with Warlords of Draenor being released this winter, the current materials are on a decline. Tons of people are still buying them because of progression through content but obviously the volume has declined and so have prices. However, this should not discourage you. When the new expansion rolls out, people will still use the "old" mats to quickly level the new professions or because they can't afford the new materials OR they don't want to justify spending more $$ on stats that aren't that much greater than what they currently have. Especially if they know they'll replacing the gear in a few days/weeks etc... 

In January/February of 2014, after 9 years of hardcore playing WoW I went on hiatus/quit the game. 2 days ago I finally returned. When I had made my departure, I gave away all of my pets(over 200K in value), my gold (40K), my raid/profession materials(3K) and was literally left with 4 silver across all of my characters. From then til now I've farmed a little bit of ore, sold gems and enchants and I'm already up to 3K. I've only spent maybe 1 hour -  2 hours of effort to get to where I am. So you figure from now til when the expansion hits, I'll be back up to 40K+.

Once the new expansion comes out, I can still profit on the old materials AND I can also take quick advantage of all of the new materials. Making money never stops! You just need to be creative and adjust your methods/attention for all of the variables within WoW.

Thanks for reading & happy hunting. ^^;