-1- Do you want the system to cost more or less then the house?
-2- How much more?
Actually I have a few things in mind based on what you said above, but honestly I have not found anything (in the U.S. market) that is sort of an all-in-one solution for the above that works well for everything. It's sort of the jack of all trades - master of none type of show thus far. BUT, as stated I don't do much work @ residential stuff so what I do know of I get by osmosis vs. immersion.
Looking to pour some of my own concrete soon and have been eyeing something reasonable similiar to what you described above. Thus far I have found more and more manufacturers are installing dry contacts, analog feedbacks, and 'smart' monitoring of trends build into their 'home' lines of products.
Example is a honeywell t-stat @ Home Depot that has an auxiliary 24vac output to signal an alarm condition (ie: heating setpoint 72° but space is exceeding greater or less then 5° from that setpoint).
A friend of mine just had a sec. system installed by ADT, it's 100% wireless (which I see as a weakness fyi..) but the control console has outputs and inputs which can be programmed through some manipulation. You could tie these inputs or outputs into your hvac system, or lighting. If doing a digital lighting control, I think some of the Lutron residential lineup has aux-inputs or dry outputs to link to other dimmers or light controls...which can be just as easily connected to a relay, etc. (just watch the inrush+static current on the relays as many solid state devices don't take well to banging relays on/off if they are intended to tie into other solid state devices).
If you really wanted to go geek on a budget, you could check out some of the X10 stuff. A gal at works hubby has installed it all over their house and she claims it handles some of the notification and temp alerting tasks and automation functions you seek with ease. I'm not sure about PC integration, but she speaks highly of it. The downside is I think there is some extended test and tune for the 'non-specitic' type home-automation things, as she did go home on more then one occasion because her alarm was calling her for nothing
Whats your budget?