Source code
http://hamradioprojects.com/authors/ac7ma/+axekey/code

Getting Started with the PICAXE:
http://www.picaxe.com/Getting-Started/PICAXE-Manuals/
http://www.picaxe.com/docs/picaxem2.pdf

Keyers and Keying Interfaces
http://en.wikipedia.org/wiki/2N7000
ARRL Handbook 2011, 24.11, “The Universal Keying Adapter”
ARRL Handbook 2011, 24.12, “The TiCK–4”

Picaxe Hardware
http://www.picaxe.com/Hardware/Starter-Packs/PICAXE–08-Starter-Pack
http://www.phanderson.com/picaxe/picaxe_rev_ed.html
http://www.sparkfun.com/categories/125
http://www.sparkfun.com/products/8313

Debouncing with the Picaxe BUTTON command
http://www.picaxe.com/BASIC-Commands/Digital-InputOutput/button/

Iambic Keying and Morse Code
http://en.wikipedia.org/wiki/Iambic_keyer
http://en.wikipedia.org/wiki/Morse_code

Ultimatic Keying
The Ultimatic, John Kaye, W6SRY, QST Febuary 1953
http://p1k.arrl.org/pubs_archive/33449

QST Article Search (ARRL member benefit)
http://www.arrl.org/arrl-periodicals-archive-search

Debouncing with the PICAXE button command
http://www.picaxe.com/BASIC-Commands/Digital-InputOutput/button/

“A Guide to Debouncing” by Jack G. Ganssle, N3ALO
http://www.ganssle.com/debouncing.htm