Ultralisks with full armor upgrades and Queen support are kinda fun. They're nigh invulnerable to the lower tier units, and the Queen can top them up easily enough. It's not even hard to Micro that. And the Anti Air capability? Icing on the cake.

Bad news is, super vulnerable to Phoenixes.

Queens + Broods with some Muta/Ling support? Oh yeah, fun times.