Infinitely many.
4
There are only four different configurations.
Ignoring rotations, there are 3 distinct solutions.
A rectangular prism that is 4 cubes by 2 cubes is made up of 8 cubes.
24 of them
13
4
There are only four different configurations.
If you have got enough cubes, as many as you like.
Ignoring rotations, there are 3 distinct solutions.
You could try 14!
3
A rectangular prism that is 4 cubes by 2 cubes is made up of 8 cubes.
about 10
25
24 of them
With no repetition of shapes (symmetry) we have obtained 26 different combinations.