Does anyone here customise their spells' appearance in D&D?

Generally you can modify the appearance of your spells as long as it doesn't effect the inner workings of the spell proper. I find it's woefully underused: why should your necromancer settle for puny beams of light for you magic missile when he can instead summon a swam of ethereal bats that swarm his enemies?

What are some cool spell appearances you guys have seen or done?