Simple question - is it possible to make a render in which the background becomes transparent, so that I can:
1: Copy and paste it on top of a photoshopped background, without having to use magic wand or whatever to delete the rest?
2: Have a semi-transparent part of my model (fighter canopy) turn out semi-transparent in photoshop as well, so that the background can be partly seen?
transparency is also known as ‘alpha’ in CG, simple enable RGBA in the render panel and chose an image format that supports alpha channels. such as PNG.
Oh, this is just sweet, thank you 
That blue background you see by default is actually transparent, so if you mouse over the render output and click and drag, you will see the RGBA values for the pixel under the mouse cursor, and can tell quickly what is transparent (A:0).