Coming to this late, as I am in the same kind of boat.
Options might be different in 2014 due to newer options for models.
I'm trying to find a nice few sets that can cover me for building almost anything else. Using rebrickable, adding models to a set and then looking at other Technic models (both official and MOC) will give you an idea of what sort of bits you want next. Also gives you suggestions on models to buy to up your % match.
8043 seems like a good set, but has 4 piddly M motors, which I guess is okay on top but on its own is a little lame, also the price for this retired model has gone INSANE.
So far I have gone with these three...
42030 Volvo L305F Wheel Loader
Got it for £131 new, has 2 remotes, various sized motors (including steering servo), actuators, bucket and some rather large wheels.
42009 Mobile Crane
Seems to be the largest model you can get for a good price (£105), has the most pieces in any Technic model so far (although apparently half of these are just pins!) but this brings another motor and battery box (sadly just 1, but still), diffs, a bunch of wheels and obviously lots of pieces.
I already own a few small (9391, 42001) and a mid sized model (80690, buckets, wheels small LA)
Recently bought this for £25 as a present, really good price, just been looking at how much track is to buy on its own and its not much less than this. Although its ~14 short of building the 8043 (and I'm guessing short of a lot of MOCs) but its a start, at least you get extra parts. Could buy 2!
Hopefully they, obviously large will be a good start.
Ideally what I personally want next is:
A proportional remote, the train sets include these + the "smaller" battery box that a lot of people use, although the big designers often have the rechargeable boxes, the 6xAAA are drop in replacements (mostly, assuming they haven't made use of the reversal pin). Im not sure I will do this though as I don't think the lad will like me gutting a train (and I don't want to stretch to two!)
Pneumatic kit, no sets seem to have a lot in them. ile9os on ebay has a VERY nice "pro" set. I wish they had more than 1 mini-pump in the collection, sadly to get 3 (to make a total of 4) from bricklink the price goes up when you have someone that has a quantity you want (bricklink is kind of a pain for that).
Steering kit, there are a few different types so looking at smaller models for these.
Springs, I'm keeping an eye out on deals of smaller Technic non motorised sets for these.
Wheels, but I'm going to resist buying them on their own though as you can easily get these on smaller models, and will eventually be overrun with them (as I am with non-Technic LEGO since I decided to buy a batch lot and later on... I have too many!)
More clutch gear, the above has some in but would like more, the crane has a lot in because it has one motor for all the functions. Service truck seems to be another and has some pneumatic kit - personally don't like that model though and I'm not sure about the price (still watching)
42005 seems to be good for steering ball joint(x2) small springs(x4) "steering arms"(x4) steering rack(x2) knobwheel(x2). All that would cost you around £20.45 on ebay at a quick glance, and has sold as low as £23 on amazon (currently £33, I'm going to hold out for sub-£27) and it has 327 parts. You can see why people buy and part out to sell.
btw for the likes of Amazon, get onto camelcamelcamel and set a LOT of "crazy" price alerts and sit on them for a long time.