As many of the blogs around here have been doing, I'm participating in the FTW community post on "must have units," units that we just can't kick out of our lists. For me, it's my stormtroopers, the Black Jacks. While a lot of people have written them off as too expensive, for me they are one of the great multitools in the Guard armory.
Want to get rid of tanks? Give them meltas and Airborne Assault and go wild. Want to eliminate Marines? Max the squad out and load up on plasma. Troops in cover keep on getting you down? Flamer stormtroopers outflanking in a heavy flamer bedecked Chimera FTW! As long as you have a specific plan in mind for them, the Glory Boys can get the job done.
In fact, I like them so much, that I've been working on a tactica for the Big Toy Soldiers. Look for it to arrive over the next couple of days.