I realise I'm probably around 6 months behind everyone else here as usual, but I managed to solo Normal Sethekk Halls earlier today. I was actually very surprised at how easy it was, since at 70, even in Normal mode, this instance was always quite challenging for me.
It was, I admit, a very slow process; probably around 2 hours. I move very slowly and deliberately when soloing instances. About the only real trouble I had was with Darkweaver Syth, and I also had momentary difficulty with the Time-Lost Controllers as well, before I figured out a good set of tactics for them.
Darkweaver Syth has around 80k health from memory, and summons probably around half a dozen elemental adds. I died a few times with him at first because of being pre-occupied with trying to get the boar to tank the adds. I eventually figured out that I simply had to mow Syth down, and his adds would vanish on their own.
My strategy, then, was to send the boar in to Syth, then very carefully manage threat, while still trying to do fast damage until he was at 50% health. At that point, I'd pull threat; so what I did then was to feign death, drop a Frost Trap, and kite the adds in order to finish Syth off.
Ikiss also has about 85k health, and was enormously easy, which I was very surprised about, given how hard I remember him having been at 70. I sent the boar to him and then opened fire, and when I pulled threat, Ikiss blinked over to me. I ran around the other side of the nearest pillar during his arcane explosion, and then came back and resumed DPS.
For most people though, I'm not sure whether to recommend instance farming for really good money. I did another Ramps run today as well, and would have been lucky to make 50g out of it, all told. I possibly just had bad luck with drops though, because I'm pretty sure I've had 100g or so from there before.
Scholo isn't really an option any more either, since most of the blues there are devalued now, and nobody seems to want Dark Runes any more, either. The most money you'll probably make from a Scholo run now will likely be 60-70g for a really full clear, and most of that will come from blue non-recipe drops, and 20g from the AH for the average five stacks of Runecloth. I wouldn't bother trying to sell the Lifestealing and other recipes for more than 5-10g on the AH now, sad to say; I haven't seen them go for more than that since pre-WoTLK.
The good news is that Quel'Danas is still viable, (IMHO anywayz) especially as an augment to the 100g or so you'll get from the Icecrown dailies. I did the island earlier today, and made 90-95g or so. You get 12-16g from all of the non-flying dailies, and with not all that much farming, I made an extra 70g on top of that from trash and greens. Netherweave is still selling at around 6g a stack, too...and I got around 5 stacks of that, as well.
The respawn rate at the island is still as ludicrously fast as it always was, too; so the amount you can make is literally determined by the length of time you're willing to farm. Clear out one area with Thunderstomp and Volley, then go and do the same in a second area, and by the time you've finished in the second area, the first will have respawned.
I find it's faster to make money there than in Northrend sometimes because the island is small. I can round up a lot of relatively weak mobs and kill them all at once, and only have to travel a short distance to reach the next area and do it again. With Northrend, for the dailies at least, the Icecrown dailies are the only ones I know of which yield more than 10g each, and for the rest of them, you also have to travel to different zones, as well.
I feel that Northrend skinning is also good. I don't get Arctic Furs dropping a lot, but I can get 30-60g each for them on my server. 10g per stack is also fairly standard for Borean Leather, and altho the cave north of K3 has been nerfed (in terms of the spawn rate) it is still fairly good for leather.
So far, according to Accountant, I managed a profit of around 300g today, and I haven't done my Icecrown dailies yet, either.
For anyone with mining, that is probably considered laughably pathetic, but I feel it's ok. Although for miners who do their dailies as well, it's just even more money, and given the size of some of the gold sinks which exist now, (the mammoth, the Dalaran ring, etc) are any of us ever really going to say no to that?