Some fun examples I recall are:
1) moving an observer above a turret that's building and it will prevent the turret from firing
2) allying your enemy so that the mines don't trigger as they walk over your spider mines and at the last second un-allying so that all mines trigger at once
3) selecting your worker's and right clicking on an unbuilt geyser twice before right clicking on an enemy unit will stack all those workers to attack the enemy unit
Are there any other's that I am missing?
Edit: nevermind found this thread //www.gmnlm.com/forum/brood-war/514740-brood-war-exploits-tricks-glitches-please-help