This is a little tuning exercise (right click and choose "save link as") similar to the commercially-available "Tuning CD."  I did it with the Harmony Director keyboard, so all the pitches are perfectly tuned to a standard of A=440.

It could be used in either of two ways:
    1) Simply play along — it's 13 notes from concert Bb to the octave above — trying to match pitch as closely as possible.
    2) Hook your instrument up to a tuner.  Don't look at the tuner during the first four counts, then look at see how successful you were in matching.  If you've got a tuner, but not a hookup, try using headphones; the tuner will pick up only your instrument and not the recording.

I'd suggest you do it throughout the full range of the instrument.  It's a wonderful ear-training technique that I'm sure you'll find beneficial.

This exercise is for a perfect 5th.  A tempered 5th, of course is seven half-steps (700 cents) wide.  A true, beatless 5th, is actually 702 cents wide.  This exercise, then, is intended to refine the player's concept of a beatless 5th in just intonation.

You'll hear 13 major triads, ascending chromatically from Bb to Bb.  After the first four beats, the other notes drop out, leaving only the 5th.  The idea is to play the fifth (concert F to start with), then look at the tuner to see if you're matching the 5th after the other notes stop.  The tuner should be calibrated to 441 for this exercise.  You might find the needle just slightly to the left of zero.

Here's the major 3rd.  A tempered 3rd is 400 cents wide, but a beatless major 3rd in just intonation is 14 cents lower, or 386 cents wide.  The routine here is the same as the last one.  Bb triad for four beats, then the 3rd alone for four.

Some of you might be as skeptical as I was about this at first.  A major third 14 cents flat?  Come on!  But then when I heard two triads side by side, one in tempered intonation and one in just intonation, I was astonished at how much better the lowered third sounded.

True, most of the time we're not even aware of what chord tone we're playing.  My hypothesis is that the best musicians are simply listening constantly to make whatever note they are playing at any given moment sound "right," and that if it's a chord tone sustained for any duration, they naturally favor lowered major 3rds and raised minor 3rds (and we're assuming, of course, that others playing the same pitch is doing exactly the same thing).

The tuner should be calibrated to A=437 for major 3rds.

Here's the minor 3rd, which is actually 16 cents higher in just intonation than in equal.  You could calibrate your tuner to A=444 for this one.  These calibrations, incidentally, are not really dead on, but they're as close as we can get and the difference is so slight as to be negligible.