CME has several series that include 76-key MIDI controllers that are very full-features, and a few of them have weighted action. The same with Studiologic (aka Fatar) and their VMK series. The 76-key versions are sometimes hard to find but I can point you to a "secret source" (they want to be word of mouth only) if you decide you want one of them. CME gear (I used to own some) has not proven reliable, unfortunately. The VMK series has splits but only one zone.
The best quality and most feature-rich controllers right now are the MPK series from Akai, but unfortunately they don't make a 76-key edition. Their 88-key board has pretty good action and is affordable. But that's probably too big and heavy for you.
Here's a cheap discontinued model from Roland that you might try to hunt down on eBay:
http://www.samash.com/p/Roland_A37%2076 ... _-49979048" onclick="window.open(this.href);return false;
A lot of people really liked that model -- although not as much as their ones from the late 80's and early 90's (those are fairly rare by now).
Another used model to look for on eBay is Oberheim's late 90's MIDI controllers (I forget the model numbers, but a search for Oberheim MIDI controller on eBay will probably get you there, if anything is available for sale currently). They had good MIDI implementations.
If you can get past the limited MIDI functionality and arcane manual, the Studiologic VMK is about as nice as they come in terms of keybed action (I owned the VMK88+ for awhile):
http://www.MIDI-store.com/Fatar-Studiol ... 16754.html" onclick="window.open(this.href);return false;
CME has three or four current models that come in 76-key editions; most of them with weighted or semi-weighted keys. The Z-series is hard to find data on, though:
http://www.MIDI-store.com/CME-VX7-USB-A ... 16191.html" onclick="window.open(this.href);return false;
http://www.guitarcenter.com/CME-Zkey-76 ... 1934790.gc" onclick="window.open(this.href);return false;
http://www.sweetwater.com/store/detail/UF70CL/" onclick="window.open(this.href);return false;
http://www.MIDI-store.com/CME-UF70-76-K ... 16883.html" onclick="window.open(this.href);return false;
As for Studiologic and Fatar, they recently came out with a new super-advanced Numa series that has fewer on-board controls but very advanced graded hammer action.
http://www.MIDI-store.com/Fatar-Studiol ... 19679.html" onclick="window.open(this.href);return false;
http://www.MIDI-store.com/Fatar-Studiol ... 18196.html" onclick="window.open(this.href);return false;
http://www.MIDI-store.com/Fatar-Studiol ... 17792.html" onclick="window.open(this.href);return false;
These are 88-key models but I'm listing them anyway in case you give up on 76-key models.
Yes, I said there are a lot of models to choose from, and there are, but they are limited to just a tiny handful of vendors, and ones that don't show up on many websites.
There's actually been some attrition lately amongst MIDI controller manufacturers -- there were more choices a few years ago. Thus, eBay might be your answer.
I think the market has dried up, except for more compact models specifically designed to be quick-sketchpad note-entry devices to always have by the computer so that you never lose an idea because of the ergonomics of turning around to use a larger keyboard or due to setting one up that wasn't ready to go.
In fact, I bought one of those myself a few weeks ago, and it is speeding up my composing and arranging as I no longer use notation editors for quick-and-dirty stuff anymore. I bought the Alesis Q25 and it has a really nice semi-weighted action. They don't make a 76-key edition though, nor does their sister company Akai.