Alain Benbassat has written a freeware program, called Functional Ear Trainer, that you can use to learn harmonic relative pitch.

Pitch Train is easy to understand, and relatively cheap.  It claims to be "the perfect tool for achieving absolute pitch"; I don't know about that, but it is able to drill tones in various configurations.  Also has a free demo for downloading.

Absolute Pitch Trainer is available from its website.

PitchCoach is available both for Macintosh and Windows.  It's freeware, which is cool, but I can't recommend the part of the program which claims to teach absolute pitch.  You're supposed to click a button, then wait ten minutes, and then guess the note it unexpectedly throws at you.  Seriously.

I downloaded Absolute Pitch from Silvawood Software and discovered that it is a harmless little application; well-intentioned, but probably not very effective.  My research suggests that tonality and structural comprehension are crucial to pitch training, and this program claims to negate both.

EarTest claims to use methods that are "scientifically proven to work".  However, according to my research, no methods have ever been scientifically proven.  But, proven or not, Ear Test provides some options for random note testing.

Pitch Paths has a melody-based approach which claims to teach "perfect pitch at any age".

David Griswold has created an audio CD for "absolute pitch memory training".  He claims that by listening to his songs in the key of A, you will memorize the musical note A.

I haven't tested BigEars, developed at the "US School of Commercial Music".  In fact, I have no idea what it does, or how it works, or why they feel the price is justified, and their website doesn't offer any clues.  I wonder if anyone buys their product.

I have also not tested "Brainwave Synchronization Technology", but I haven't seen this theory anywhere else.

Graham English's hypnosis CDs are definitely unique, but I have neither proof nor disconfirmation of their effectiveness.  I have to admit I am truly awed by this man's skill at writing hard-sell advertisement.