Here are some hobby projects I've done involving measurements and electronics.
Time measuring elapsed time, time intervals, frequency, and so forth
Zipit Z2 small, cheap, has wifi, runs Linux
Light Levels using Arduino-compatible JeeNode with LuxPlug (Nov. 2010)
Battery Charging and discharging curves (NiMH)
USB power from external battery pack (for HiMD device)
Audio measurements of digital recorders.
Fuji F700 vs Canon D60 image comparison.
Canon D60 digital SLR intensity transfer curve.
Vivitar 285HV 12V supply for a faster flash recycle time: pro and con.
Sharp MD-MS702 MiniDisc recorder noise.
Aiwa AM-C80 MiniDisc recorder noise.
Geiger Counter radiation measurement.
Geiger Counters for measuring alpha, beta, gamma & X rays.
Car Counter measuring car speed/size/acceleration.Heart Rate Monitor sends short range FM signal for external monitor / recording
Fluxgate measuring magnetic fields.
Spectrum of a compact fluorescent light.
Spectrum of a UV LED flashlight.
Floor Fan output measurements.
Akai DPS16 modification for lower acoustic noise.
Ballistics project long ago, a few pages from it.
Source miscellaneous hardware-interfacing source code.
is a very useful reference on many aspects of electronics.