I'm a really big fan of the animal shaped humidifiers made by Crane. Bed Bath and Beyond and Target carry them and I think they're $30. I've seen them on Amazon too. They're pretty simple to take care of...no filter or anything to worry about. Mine gets build up from hard water sometimes, but that would affect any humidifier. I just rinse it out the base every little bit and it's good to go...the tank stays pretty clean.
The penguin is set up differently from the others and it a little more annoying. We currently have the frog and I really love it. It's also really quiet!