Chase sanborne has a book and cd out called tuning tactics. While it's a huge plug for using a centre pitch tuner, it also has the recording which is a series of drones against which one would practice first matching pitches and then working with harmony notes (Scottish music anyone?). A neat tool. Could be achieved with any keyboard while holding down the sustain pedal. It's a great exercise to really hear what thirds and fourths, etc. Sound like. On that note, it's not a good idea to match each note on a piano or keyboard instrument since these instruments are tuned in an approximation of pure harmonies. Tune one or two notes as suggested (c & g) and then use those things that help keep your glasses from falling off.