There are four kinds of Technics SL-1200 widely available today. The first is the SL1200MKII. The most incredibly annoying thing about it is the detent in the pitch control slider, where pitch adjust = 0%. This would not be a problem at all, except when you are trying to match two records whose pitches are off by about 0.1% and the slider kicks right to 0.
The SL1200MK3D thankfully does away with this detent, and also adds a button to temporarily change the pitch back to 0%, called "Pitch Lock". The power switch is recessed just enough to prevent accidental power-offs. Unfortunately, the torque on this model is a bit lower than the MKII.
The SL1200MK4, only available in Japan, adds a reverse switch to the MK3D.
The SL1210 is supposed to be available only in Europe, and they certainly are more common there. The SL1210 is identical to the SL1200, except for the color. SL1200s are silver, while SL1210s are black. They are the Winterfresh version of the 1200.
In 2002, Technics released the SL1200 MK5, which has the reverse switch of the MK4 and the black casing of the SL1210. Two more bits of style were added to these beasts; the pop-up target light was changed to a blue bulb, and a line of blue accent lights now appears along the pitch slider. These are probably mostly found in Japan.
When a Technics deck's stop button is pressed, a brake kicks in and the platter stops quickly. On 1200s and 1210s, there is a little potentiometer that adjusts the force of this brake, and on a new deck, you can set it high enough to make the platter bounce off of the brake and spin backwards. (thanks sakke)