If you don't care about pharming raw materials, then I'd say tailor/enchanter.
Tailoring gives you the Frozen Shadow armor and the 28 slot soul bag (along with all of the other bags) and all kinds of other nifty armor you can make for yourself or others.
Enchanting is VERY nice for enhancing any and all gear you get, be it from tailoring or drops.
These two skills mesh well since as you skill up your tailoring, you can DE anything you make and use that to skill up your enchanting - basically getting two for one.
Tailoring also requires a lot of enchanting mats, so you make an item, DE it, then use the dust from that DE to make another item.
Also, as mentioned above, the surplus dust, shards, etc you get are wonderful money makers even if you don't need the cash.
These two are also the easiest skills to pharm up fast - start at the low end instances and just solo them and save only the greens and the cloth drops - rinse and repeat till you don't need the mats anymore and move on to the next higher instance - at 70th level, you should be able to clear any pre-50 instance with ease and most 50-60 instances most of the way with a bit of caution.
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Second is jewelery making and mining.
The jewelery you can make at any level is fantastic, plus, you can also hook up your alts and friends with the stuff.
Being able to cut your own gems at Outland levels is also a godsend.
What I can say is that getting mining up is a miserable experience - even worse then herbalism - and if you try to AH things you're going to easily spend the cost of an epic mount just trying to get your engineering/mining to Outland levels.
As a plus point, you'll make a fortune on AHing your own ore/gem leftovers, but you said you didn't care about profit.
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Third recomendation would be herbalism and alchemy.
These two skills are going to be SOBs to train up as the choice is either AHing the mats or riding around newby zones all day looking for herbs - not nearly half as fun as soloing an instance.
The potions that you can make at all levels are useful - having a 70 lock myself, having a good supply of mana/heal potions when things go horribly, horribly, horribly wrong is nice.
The armor and stat potions also rock.
Being able to make any and all potions for friends and alts also makes you rather popular and once you get to Outland grade herbalism, once again there's good money to be made putting spare herbs onto the AH.
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Fourth recomendation is engineering and I don't really recommend it for a lock - especially if you're starting from scratch.
Yeah - there's a lot of neat toys, but personally, between pets, nukes, dots and wands, I don't really think engineering could have helped my lock much.
I confess that I haven't gotten it past 225 on any alts yet, so its possible that higher level engineering might hold some appeal for a 70 lock.
As with JC, getting your mining skill up will suck balls but you'll make a killing on the excess ore/gems.
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Leather working and Blacksmithing are worthless to you as a warlock - LW makes nothing you can use but armor patches and smithing only makes a handful of swords and daggers that you may or maynot find of use. All said though, the small value those two skills will provide you as a warlock will never justify the cost of leveling them.