Remember that game, old one, you have never ever finished ? Maybe you can see it now!
http://speeddemosarchive.com/
http://bisqwit.iki.fi/nesvideos/
You have many, many games.
Eg:
DOOM3
RESIDENT EVIL 4
SONIC 2 (GENESIS)
SUPER CONTRA 3 (SNES)
Most of them are time attack! They try to finish them at the minimum time as possible! Very very interesting. They even look at RAM states of emulators calculating every damage to know how to perform at best! (this quote is from a game(TMNT4 - SNES), I will try to find it again and post here.)
ps: do you know more sites like these ones ? Post them!