On this topic I have recently pondered myself.

Here is what I would like to do:
1) use a laptop to display output
2) graph the output in real time
    This allows observation of trends in the short time frame, such 
as oil temperature as affected by startup, hill driving, on hot days, 
etc.  
3) retention of data for later analysis (spreadsheet or such)

For thermal data (temperature) there are two types of measuring 
devices applicable for use in our temperature ranges (there are 
others)

Thermocouples indicate temperature by the generation of millivolts 
due to dissimilar metals at the junction (end) of thermocouple (TC) 
wire generating electricity.  A guage is available for direct reading 
of temperature.  Requires conversion from analog to digital for input 
to a laptop.

Resistance temperature measurement (typically used by VDO and others) 
supplies a voltage to wires and measures the change in resistance due 
to temperature.  Requires conversion to digital.

TC's are readily available, can be installed easily and are relatively 
cheap.

I can envision wiring up a bunch of TC's to gather temperature data:
outside air, engine compartment air, head, oil, cooling area around 
cylinders, cab, rear cab, coolant tank, coolant at radiator, etc.!

BTW, most of the technology for doing this stuff is readily available 
though places like Omega (on-line) but is pricey.  With the 
collective knowledge of the computer, hardware, controls, etc types 
on the list(s) we should be able to pull something like this off.

Haven't pondered about pressure data yet.

- Jeff