Tom Kranis recently released his mappack containing rejected levels and cutscenes. I was first made aware of Tom Kranis when he released his very interesting Halflife 2 map entitled "A Dog Was Hit In The Head With An Ax". Of the cutscenes, included are scenes of Dog getting hit in the head with a BSP-designed axe, Dr. Breen giving his famous 'Carbon Stars' speech in various locales, and lots of other stuff. If anything, I'd say that 90 percent of the mappack is rubbish, but it's definitely worth checking out if you're into mapping as there are really cool effects, gameplay concepts and ideas that have not been seen in any other Halflife 2 mod (remote controlled scientists, an automatic oil drum launcher, npc who follows you and wears a machinegun on his head that you can control, just to name a few) in addition to humourous cinematography (most of which I've recorded so you don't have to go through them).
Be sure to watch this video walkthrough of "A Dog Was Hit In The Head With An Axe." Worth checking out if you can't bring yourself to finish the map all the way through.