Most highschool kids and some college have a TI-83(+) for math, so some of you may be interested in this. Basically, there are 2 languages for the Ti-83+. Basic and z80 assembly. Basic is easier, but asm is alot faster and more powerful. *note* With z80 assembly, you can make some realy awesome calculator games.
Actually, z80 assembly is almost identical to the language used to program the gameboy. Anyways, Ticalc.org is a really cool site with thousands of games to download for the Texas Instrument calculators.
Maxcoderz is a great programming group for the TI-83(+) and this is their forum. z80 Revelation is my programming group. This is a great tutorial for those of you interested in programming z80 assembly.

Also, z80 assembly does not differ that much from x86 assembly used on computers, and it is a great steppin stone. All of your tutorials that you mentioned here are great, especially the 28 days one. I would recommend to everyone interested to find a more recent version of TASM than the one provided with the 28 days tutorial. The most recent version is version five and is packaged with Borland C++, but version 4 can be found elsewhere. Keep in mind that Borland has never given permission to anyone to distribute TASM, and other free assemblers allow assmebly of z80 code as well. One of those would be a better alternative.