For now, I've only looked at the parent set [tekken], but it should be easy to duplicate for each clone.
The time I've been offline I've been fiddling around with the Tekken series in MAME 0.117 (now finally updated).
Looking at 264948, 265950 and 266600 in RAM, these locations display a 32-bit number, seemingly a pointer for the animation data - animation, position of character and maybe collision. On the player 2 side, they're at 265978, 265980 and 266690.
Adding these three identical values and turning them on makes the character do the move in a looped fashion.
Info of moves can be found here. You'll also find Tekken 2 (Ver.A only) and Tekken 3 (Ver.B only) on the site.
If someone is interested, maybe we could try to find what drives these moves and somehow assign them to a cheat. One problem I've thought of is, unlike Street Fighter II, Tekken relies heavily on combination attacks, rather than single special moves (like a hadouken or shoryuken). The animations only display each individual move though, so a move can be cancelled, so a 3 hit combo like Michelle's 'G-Clef Cannon' has 3 different animations for each punch in this case, but you can of course only do 1 or 2 punches by not inputting the extra button(s).
I wouldn't mind making a small move list cheat, which only has the special/unblockable and complex moves (like Nina's 'Back Hand Slap' multi-part combo), and the 10 hit combos for new/intermediate players who seem to have a bit of trouble with timing and 'perfect' button hammering!
For instance, setting the three above addresses to 0x80114DD0, your character (anyone) will perform a Yoshimitsu sword stab, in a looped fashion if it's kept on. However, it won't do anything as it's just the animation. Your opponent won't lose half their energy and fall over (with the 0x80102D10 animation). We need the part before it - the trigger, and some magic for the combos, which need sequential button presses for each part of the move (e.g. back, back, left punch for this move), which the cheat engine may or may not be able to currently do.
Update: Setting some sort of activation key might be the only way do this, leaving the MAMEr madly hitting these keys instead and making it totally useless. It might only be useful for 'easy' multi part combo cheats in Tekken 2 (e.g. King's Standing Heel Hold -> Indian Death Lock -> King's Bridge - f,d/f+2+3, 1+2,1,3,1+2+4, 1+2,3,4,1+2,1+2+3+4 - try madly hitting that on a keyboard(!) in the short time span during each move). Luckily I have the Dual Action controller and access to the 'P' key!

Each button press is detected in approximately the first 3-5 frames, counting on/off style (tap 1) and on/hold styles (hold 1, then hit 2 while still holding 1 (1+2)).
It still isn't the one button -alities as you would find on the console versions of Mortal Kombat. It would be really nice to have one button 10-hit combos though!
Edit 18/05/2012: Updated info on pointers.