I am a BIG FAN of the Jerry Ziliak High Speed Morse Code System.
These were originally on cassette tape, but after Jerry Ziliak passed away, his estate must have licensed the transfer to CD and now Amazon sells them.
His theory is simple: He teaches you each letter, number and character one at a time at 20 WPM sending of the dots and dashes.
But as he expands to words, he sends each character at 20 WPM, but by putting in more space between letters, he starts out at 5 WPM.
Then as you get comfortable, he starts to "increase" the speed by deleting some of the spacing.
In this way, your brain hears 20 WPM right from the start, instead of other teaching methods that make you relearn each letter, etc., as your speed increases.
I can send you a sample if you like; send me a PM.