For OpenBSD 4.1, Grange@ commited my patch (thanks!) for a new driver owsbm which adds support for the DS2438 (1-Wire Smart Battery monitor). The driver supports the basic A/D functions for getting the three voltages (VDD, VAD, and CR) and the temperature.
demeter:~ linville$ sysctl hw.sensors hw.sensors.owtemp0.temp0=22.75 degC hw.sensors.owsbm0.temp0=22.34 degC (Temp) hw.sensors.owsbm0.volt0=4.82 VDC (VDD) hw.sensors.owsbm0.volt1=1.59 VDC (VAD) hw.sensors.owsbm0.volt2=0.00 VDC (CR) hw.sensors.owid0.raw0=2541210 (ID) demeter:~ linville$
I've written a couple small daemons to dump the temperature values into a database. The DS2438 is wired up to an HIH-3605 humidity sensor. VDD is the power supply voltage. VAD is the output from the HIH-3605 and is proportional to the power supply voltage. Here is a paper describing the use of a DS2438 and HIH-3605 to measure humidity. CR is the voltage across two pins and is used to calculate the current (in the case of the circuit I have, it's used to measure solar radiation). If you're interested in this setup, it is a Hobby-Board HTS3-R1-A (Humidity/Temp/Solar). It has been working quite well for me.
A quick PHP script later and we have a really nice graph of the temperature. You'll need an SVG capable browser to view it like Firefox, Opera or Safari. I'll put all the sources up once I remove the hardcoded badness. :-)
Both sensors (owtemp and owsbm) are on the same board and are currently placed right above a vent in my apartment. The spikes in temperature are when the heat pump turns on.