I have worked on the following platforms:

Power 3-II:

Perf counters via pmapi
Power measurement via self designed socket
First take on curve fit / regression model
Sampling by TeraTerm

Pentium Pro:

Perf counters via kernel hack
Power measurement via shunt R
Thermal modeling by concurrent thread
Monitoring over CASTLE
Sampling at context switch

Pentium IV:

Perf counters via LKM
Remote monitoring over ethernet
Power measurement via current probe/DMM
Power Modeling via remote monitor
Sampling at sleep timer

Perf counters & Basic blocks by dynamic instrumentation via Pin
Local Power Measurement via current probe/DMM serial device file
Sampling at trace boundaries/instructions

POWER4:

Perf counters via ticker/pmapi
Sampling at context switch

G5:

Perf counters via EASY/CHUD
Sampling at timer?

Pentium M:

Perf counters via LKM/kernel hack
Power Measurement via shunt R
Sampling at PMI interrupt

Woodcrest/Irwindale/Dempsey/Sosssaman:

CMP/SMT processors: Merom/Yonah/NetBurst
Perf counters via EMON
Power Measurement via Extech from wall
Sampling at timer with multicores