Well, aside from fungus, none come immediately to mind. In any case, once houseplant enthusiasts accept that assumption and do their level best to make their indoor jungle feel like it's outdoors, the happier and healthier plants are going to be. But that does not mean watering them every time you have a drink of water. The unanimous opinion of every horticulturist I've talked to is that over watering is the biggest killer of houseplants.
Passion flowers are big, too.
A lot of them bloom real well in a pot. And there's a brand new Plectranthus hilliardiae with succulent foliage that has a slightly nutty fragrance and flowers in a wonderful baby blue. My favorites are the winter-blooming bougainvilleas that come in discreet colors like white, salmon and gold. It's amazing how little care they take, and they still perform. Renee Kroeger, greenhouse manager for Fountain Square Nursery in Citrus Heights, agrees that over watering is the biggest single killer of house plants, sometimes caused by planting in pots with no drainage or putting a pot with drainage within another decorative container that has no drain hole.