Allthough every Amiga keyboard uses the same "protocol", due to the different physical connectors or wirings they are meant to be used with a specific Amiga model.
Most keyboards use Mutsumi keycaps that can be swapped around, but other types of keycaps do exists.

Here's how you can quickly determine the type of keyboard and keycaps.

Amiga 500

The Amige 500 has 3 types of keyboard: 

• Mitsumi keyboard. They are found in 99% of all Amiga 500 and 100% of all Amiga 1200.
• Samsung keyboard. The keycaps look very similar, but they are not the same and you can't use them on a mitsumi keyboard.
  
  On the left: Mitsume keycap, on the right: Samsung keycap
  
  
• Hi-Tek keyboard: These can be found on early Amiga 500 models. They are true "mechanical" keyboards with a seperate switch for each key.
  The early models have a "Commodore" key as left Amiga key.
  They are nicknamed "space-invader" because of the shape of the switches.
  They are quite sought-after, because
  • They are mechanical and are closer to what we nowadays percieve as a quality keyboard: typing is less "spongee" then on Mitsumi or Samsung keyboards.
  • That are made of PBT and don't yellow, unlike the ABS ones of the Mitsumis that turn yellow after some years.

Amiga 600

All Amiga 600 keyboards have Mitsumi keycaps. They can be switched with the keycaps of the 500 and the 2000, except for the spacebar and the shift keys (which are shorter on a 600)

Amiga 1000

The Amiga 1000 has a square RJ-11 connector.
You can easely recognise them on the "cross" shape of the cursor keys and the square Amiga tick logo at the top-right corner.
They have red Amiga Keys and Cherry switches (but the keycaps are not Cherry MX)

Amiga 1200

All Amiga 1200 keyboards have Mitsumi keycaps. They can be switched with the keycaps of the 500 and the 2000

Amiga 2000

The Amiga 2000 keyboard can be recognised by the absence of stripes on the case.
They have a large 5-pin DIN conector.
There are multiple variants.
Some early models have red Amiga buttons instead of black ones.
The keycaps can be

• Mitsumi: the keycaps can be switched with a 500 or 1200 model, but usually underneatch the keys are rubber domes instead of metal springs.
• Hi-Tek mechanical switches. These have a Commodore logo at the left Amiga Key.
• Cherry mechanical switches, found on the most early models of the 2000 and more or less based on the Amiga 1000 keyboard. They have red Amiga keys and a Caps-lock key with a square light at the center bottom instead of a round one at the top-right. (Quite rare) 

The keyboard can also be used on a 3000 and 4000T

Amiga 3000

The Amiga 3000 keyboard can be recognised by the stripes at the top and is beige.
It has a large 5-pin DIN conector.
It can also be used on a 2000 and 4000T

Amiga 4000

The Amiga 4000 keyboard can be recognised by the stripes at the top and is much lighter than a 3000 keyboard
If it has a small DIN connector, it was meant for the 4000 Desktop.
If it has a large 5-pin DIN conector, it was meant for the 4000 Tower.
The one with the small connector can also be used with a CD32.
The one with the large connector can also be used on a 2000 or 3000

Amiga CDTV

The Amiga CDTV has a black keyboard, very similar to the 4000 keyboard (with stripes at the top)
It has a small DIN connector but it is not compatible with the 4000 or the CD32 without the modification of swapping 2 wires.
On early models the keycaps are not black, on later models the entire keyboard is black, including the keys.
The keycaps are Mitsumi and can be swapped with 500/1200/2000 keycaps.

Amiga CD32

The Amiga CD32 never had an "official" keyboard.
You can use a 4000 keyboard.
There are also keyboards produced by a 3rth party but they are extremely rare.
(Like an insane-amount-of-euro type rare)
These are the same shape as CDTV keyboards but with the gray/black color scheme of the CD32 and another logo at the top-right corner.
The keyboard connector on the side of the CD32 doubles as serial port.