Quick Gold Tips
Alright, this has probably been stated a hundred times, and it's a point that needs to be rammed home because it is awesome for making gold.
Materials:
Since Cataclysm is coming, and we all know the hype and how people wish to get their professions maxed (I've seen that in so many guides) there are some mats that though easy to get, some people will still pay stupid amounts of cash for.
Wool Cloth: Horde this is for you, since unlike Alliance most of the mobs in low level zones aren't humanoids, this cloth drop is not nearly as frequent. Even now before Cata, some realms have stupidly high priced wool.
Low level gems: Everyone thinks that only epic gems are worth it, on my server I know gems such as "Tigerseye" "Moss Agate" go for 10g+ a gem, for something your alts could pick up in a dungeon, or you could easily prospect from cheap low level ore.
Enchanting mats: Now, low level mats for these will sell decently, but here we want to focus on higher level mats. Why? Because people are going to want EVERY single advantage they can get to getting to 85 first, that means top level enchants, etc... So, getting mats for popular enchants like Berserker is a worthwhile investment.
This is something I think is rather original and I haven't seen it yet it any guides --->
Inscription: With the addition of medium glyphs and aesthetic glyphs, many new players will be leveling this profession. And, I mean a LOT of new players. Focus on mid range mats, anything that is slightly more difficult to farm, and make sure to wait till Cata to sell them.
For those of you inclined to farming with bots, use this in tandem with these strategies. Pick yourself up a nice cheap bot like Gpbot, then go to lower level areas and farm tons of Mithril, SILVER (I can't stress enough how silver makes awesome cash, I've seen days where a single ore sells up to 89g+) thorium, adamantite, ore's that are harder to farm for the average player, they will be willing to splurge a little more on these then say Iron, or Cobalt.
Level those professions now! You want to get to 450 in professions such as Enchanting and Jewelcrafting now, when people hit 85 they are going to be doing anything they can to get an edge in raiding or pvp so they will spend stupid amounts of money on high level stuff, so if you are not one of those people inclined to realm firsts, take the time to get your professions maxed.
Death Knights: If you do not have a death knight, I suggest rolling one, getting it to 60 and making it a mule. by mule, I mean a character who you can easily level a profession on, and they come with a lot of free bag space for holding items. This is much faster then leveling a whole new character for a profession you want.
For those raiders, I see achievement raid runs becoming quite popular. Many achievements such as getting your vanquisher mounts may be gone come Cataclysm and people are willing to pay to get an efficient run through to get these mounts and items before the x-pac. Since these are rarely raided fully anymore this is a decent money maker for raiding guilds.
Are you bored? Don't feel like farming or raiding? Try low level dungeon runs. A lot of players are going to be rushing to hit 80 before Cata, they will be paying 50g+ for dungeon runs, and sometimes they don't even want the items! That's a bunch of cloth, enchanting mats, etc and a 50g tip. Sounds like something I wouldn't pass up.
So all in all, basic tips. Just stressing a point that some items will be sold for stupidly high prices because of laziness so be aware and stock up.