So as I mentioned a bit back, I can't really do dailies on my server any more due to the place being a warzone more or less continually now.
Since patch 2.4 came out until recently, I'd actually given up soloing Scholo in favour of the dailies, but now I've taken it back up again. From what I've been able to work out though, you can get more or less the same amount of money from Scholo in roughly the same amount of time as it would take to do the Sunwell dailies.
Trash farming Scholo up to the Great Ossuary probably takes around 30-45 mins if you're fast, and if you do that twice you'll get:-
10 x stack of 20 Runecloth @ 2g 80s ea (Wowecon price) = 28g.
~12 x vendor trash @ ~2g ea = 24-26g.
2 x Dark Rune @ 15g ea = 30g.
4 greens @ ~2g ea = 8-10g.
Total = 90g.
The above numbers are also conservative. The Wowecon price is very low for Runecloth; I use it when I want guaranteed sales, but on my server it can spike to 6-8g a stack at times. The Dark Rune price is another extremely conservative sure-fire sale number as well; again, I've seen them spike to around 40g at times, so 3 of those at 40g would be 120, from them alone.
The other thing I'm not counting here is that you can sometimes get blues which will go for anywhere between 2 and 50g, depending on what it is and what the market's doing. If you've got Priests going through 60, the Codex of Fortitude from there can spike to at least 15-20g, and the Wildheart and Dreadmist Druid and Priest sets drop in there as well. They're blues, and will typically go for 2g apiece, minimum. Again, depending on how many people you have at that level range on your server, they can go up to 10-15.
I also just had a Five of Beasts card drop as well, and the Wowecon median for that is 20g, which is almost the equivalent of having an entire Primal Water drop at once.
All of the above also assumes you don't have Enchanting. ;-)
If you're on the way back from a Kara raid, I wouldn't entirely rule out the Sunken Temple for some quick and easy farming, as well. Although the place's loot table is terrible, one thing which that instance is a great source of is Mageweave Cloth, and on my server the AH's stocks of that are nearly always low. The median for it is around 4g per stack of 20, and you can get prolly 10 stacks in half an hour or so in ST. The blues there are soulbound and not that great, but if you've got Enchanting you can disenchant them and sell the mats, and ST actually has quite a lot of skinning opportunities as well.
I've read extremely good things on the forums about Dire Maul North and East also; I haven't checked that out yet, but possibly will at some point today. I've been wanting to find some really good farming options, because the buy low, sell high thing really hasn't been working well for me, I will admit.
From what I'm seeing so far, the truly big money is actually often in things from Azeroth, that are wanted by twinks or people who are levelling alts, but which generally aren't available because most people don't try and get them. Hence, low supply + high demand = money. The biggest single example of this that I've seen, is a herb in Azshara and Felwood called Dreamfoil. The median price for that is 1g 16s for a single piece, or 23g 20s for a stack of 20; and Azshara and Felwood are both covered in it. (http://mapwow.com/)
The other overall benefit of soloing instances is the lack of competition. Even before Quel'Danas became as active in PvP terms on my server, there were often the equivalent of traffic jams, as there could literally be one player for every mob at times. Soloing an instance, you've got the whole place to yourself, which means no competition on drops, and also increased speed and efficiency.