Materials ('mats') - items that get used in professions. This is driven more by use than by source; for example, copper is very easy to mine, but it is widely in demand, and you can often find bargains in copper, bargains you can profit from. Contrarily, some very scarce mats may have low demand, may only be used in one mediocre recipe, and may not sell.
SSC has been known for it's abundance of pet drops, which is why this farming spot exists. It can only be done once a week by each of your characters, so make sure to hit it if you can. Generally you'll want to kill all the bosses for a chance at their rare pets. Everytime I go, I have the luck of getting one, in the video I actially got the Tideskipper to drop, and a video I done on the spot before that, I got the tainted waveling. So yeah. It's a pretty awesome spot with high rewards and also some world drops. I was able to snag a will of edward the odd as well, totalling a nasty 35,000g. The most important part is that you kill the bosses, the pet drops do sell, and they are very easy to get. Well worth the time invested.
If i start on a new realms, I am farming a lot of transmog from classic and Burning Crusade Dungeons and Raids. In the beginning, i start to post them if they have at least a DBRegionMarketAvg (Average value of an item on all EU realms of the last 14 days) of 500 Gold. All the other items get vendored. The time you hit a stock of 1000 Items, my value treshold raises to around 2.500 Gold. All the items below that value get vendored aswell. Newly farmed items that are above these treshold will be listed. Why? If I start over somewhere, I want to get a certain amount of gold quickly. Cheap items are great for that. Later on, to save time, Quality is better than quantity. As mentioned above, re-posting the items on the auction house takes quite a bit of time. At this point, I can recommend you the TradeSkillMaster AddOn, it makes your auction house work really a hell of a lot easier.