The kit I built has been pretty fun to play with, and I've got about 6 letters so far that I remember the code for and what letter it represents. There are a few more codes where I have to think about what letter it represents. I'll be able to start testing myself by listening to some code and trying to interpret it.
In the meantime, I thought it would be cool to start experimenting with the basic kit. Stopped by Radio Shack yesterday and was able to find all the circuit components and a breadboard to recreate a second key. The plan is to lay out the key on the breadboard and get it working, then experiment with some mods. First mod I'd like to try is to insert an LED that lights up when the key is pressed so that it blinks as well as beeps. Then maybe add some volume control. I think there's a good bit of room for playing with the kit.
I'm also going to need some parts bins for the workbench.