Back when I just barely had an inkling of what a rep grind was I knew the one faction I wanted to become Exalted with above all others. Since I was a druid, that faction would be the Cenarion Circle.
Of course later I would learn that particular faction was a complete pain in the ass to grind rep for, and despite being a druid I was still only Friendly when the siren call of Outland pulled me away, but the thought always lingered in my mind.
After patch 2.2 the rep grind became easier, and, most importantly, I found out about the Guardian of Cenarius title in patch 3.0.2 that could be earned by being Exalted with both the Cenarion Circle and the Cenarion Expedition. Suddenly, I had motivation. My CE rep was already Exalted and had been for a while now and it only made sense that Hana would be a Guardian of Cenarius, so I packed up all the CC rep items I still had in my bank (and there were a fair bit) and headed for Silithus.
The rep grind was surprisingly easy. I knocked out about 12000 rep my first night, though granted some of that was aided by the leftovers in my bank. Also, in these more modern times, I was able to leave Gillien by the Auction House to buy whichever pieces of Twilight Cultist set Hana needed to summon an elemental templar. With instant mail, filling out the missing pieces was much easier (except when the AH was empty of what I needed :().
The real jump in the rep gain is due to the increased value in the [Encrypted Twilight Text] turn in. 10 sheets of text are now a whopping 500 rep!
Plus, there is a semi-wandering mob on a "relatively" short respawn timer (estimated 20-30 min) called the Twilight Prophetess. She's not worth much to a 70 by herself, but she's guaranteed to drop 7-10 pieces of text, so each time you pop her off she's worth 350-500 rep! She spawns in one of two areas, both near Twilight Cultist camps, so here's a good way to grind:
* Find a Twilight Prophet. Kill and loot her. Win!
* Go to the other Twilight Cultist camp and kill random Cultists for their set pieces and encrypted text.
* Whenever you get a complete set of Twilight Trappings summon the elemental templars and loot their Abyssal Crests
* When Twilight Prophet pats by, kill her again!
* Move back to the other camp.
Whenever your bags are full, head back to Cenarion Hold and hand in any texts, crests, and sell stuff.
If you happen to have leftover Cenarion Combat, Logistic, or Tactical Badges it may be worth trying to get the an equal number of each, because every time one of each is turned in, that's another 1000 rep. I wouldn't try this if you don't already have badges though.
I went and did some Combat quests because I was short combat badges and even doing four of them at the same time, I wasn't nearly as productive as I was while I was getting texts and crests. Because I could get 1000 rep for turning in one of each on top of the rep for the quest itself, what ended up being a mission to kill 120 silithid for four badges worked out in my favor, but if I didn't already have other badges waiting to be used it wouldn't have been worth it.
And now two side notes...
Note 1: Patching up to 3.0.2 was a pain and I had to clear out about 6 gigs worth of space on my hard drive to give just enough room for the patch to install. Now it's installed and I suddenly have 8 gigs free. What the heck is up with that?
Note 2: I got the Out With It achievement already even though the Halloween event is not scheduled to begin until the 18th. How? I'm an insane person who uses a mailbox as extra bag space. I routinely shuffle a fair amount of items between Hana and Gillien (who, being hybrids, traditionally never had any bag space) and among them those items was a stack of about 17 [Tricky Treat] leftover from last Halloween. :) What I had leftover after getting both Hana and Gillien sick I sent off to my guildies.