Fingertip-to-floor test and Schober's test are the classic measurements for lumbar spine mobility. They are reproducible and still valid today for the range of lumbar flexion. Rotation and side bending of the lumbar spine are difficult to measure separately from the total spinal rotation and side bending. They are usually measured in toto.
There is a similar instrument to Cervical ROM (a glasses with inclinometres in different positions) to measure in last thoracic vertebrae (T12) and Lumbar one. I had a vey good reliability with this instrument with individual intraclass coeficient in all movements. Flexion, Extension and side bending are easy a reproductible with a good methodology, but for rotations, instead the reliability, I think is not a very good instrument because the magnet system.
3-Space Fastrak, Polhemus Inc. (see also Liberty). This instrument is an electromagnetic three-dimensional tracking system that is able to locate the position and orientation of up to four small, remote sensors. This system consists of three components: a system electronic unit, four independent sensors, and a source. The source generates a low-frequency magnetic field, which is detected by the sensors. The system electronic unit performs the calculations to compute position and orientation of each sensor relative to the source. The lumbar spine sagittal plane (flexion/extension) angles (measured in degrees) can be easily derived from two sensors strapped in place over the sacrum (S1) and L1.
There are several papers. For instance, check this one (open access):
Van Herp G, Rowe P, Salter P, Paul JP. Three-dimensional lumbar spinal kinematics: a study of range of movement in 100 healthy subjects aged 20 to 60+ years. Rheumatology (Oxford). 2000 Dec;39(12):1337-40.