http://en.wikipedia.org/wiki/StarCraft:_GhostI was checking this out the other day and then the Idea hit me that making some of the new units (scroll down a bit) wouldn't be too hard to do. I'm not too experienced at modding, and I will give an attempt, but I'm sharing this idea with you guys who are, far more experienced than I. For example, to make a Stinger, you could replace the goliath with the siege tank base and its head with the vulture body, and then change its weapons.
Or a grizzly could be made by giving an anti ground bomb weapon and then by changing some of the ground units' sizes (good luck with exactly three though.)
I'll be waiting on some new modding tools before I even make an attempt at adding more than 3 weapons to certain units. Maybe if I start with ICECC I can (probably easily) add a melee attack to the hydralisk.
So the idea is really quite open to anyone.
(Sorry if this has been done before, I just woke up. Did a quick check to see if anyone had this, and I didn't find any topics on it. A QUICK check.)