TI-83 Basic was the first programming language I really felt like I had mastered. For a while in my first CS college class I was writing code in TI basic and translating it to C++. Drugwars and Bowling were the two really impressive games written in TI-Basic.

But discovering z80 assembly was like magic. It was incredibly exciting to go to my dad's office at the university where he worked (where computers had 2 T1 internet lines) to download and try assembly games when they first burst on the scene (I was in 8th grade). Bill Nagel blew my mind with Turbo Breakout and Snake, and later AShell, Penguins, and grayscale Mario... but the best executed and most replayable games I think were Sqrxz and ZTetris on the TI-86 by Jimmy Mardell. Honorable mention to Galaxian and Falldown. I once downloaded the z80 assembly source for a game, printed it to about an inch of paper, and carried it around for weeks trying to understand it...

It was also really cool for some reason (and would often brick the calculator until you took the batteries out) to type random hex pairs into a program and execute it as assembly. "C063" run as assembly - syntax was the random looking Send(9PrgmA where PrgmA is where you typed the hex code - on a TI-83 would scroll tons of random text in an infinite loop.

Does anyone remember the TI website wars? TI Files (later TI Philes) was "so much more awesome" than "the lowly weak ticalc.org"... but look which one is still around :-)