At the moment I've got 7 aloe's (all from the same mother plant!), 2 spider plants, 2 trandescanthia, 1 calathea, 1 jasmin and 1 peace lily, a tobacco plant and a dracena. I only recently moved in here though, so hopefully I'll get more soon .
Firstly, I wouldn't go for a diffenbachia, it's also known as dumb cane as the sap can cause paralysis of the throat, but they are often sold as houseplants, they're really common. In fact a lot of house plants can cause adverse reactions if eaten so I think you are right in looking for one to keep up off the floor, for now.
Spider plants are easy to care for, they're good for hanging, or will droop down quite happily from a window sill, they are good 'air cleansers'. Jasmin has a beautiful scent when it flowers in winter. Aloes are also really easy to care for and have many uses (the 'gel' inside the leaves is great for burns (and sunburn), rashes, and insect bites, though not recommended for use by pregnant women). Peace lily's are lovely but can be a touch tempermental. The Calathea (cora) is fantastic, it's really striking and folds it's leaves upwards at night to show the purple undersides, it proving easy to care for but currently stands at about 3' tall. Dracena is like a little tree (DH likes it, I'm not so keen but it is easy to keep).
Most houseplants like a relatively warm and well ventilated atmosphere. Most like some sun but most burn in direct, strong sunlight (a net curtain or bamboo blind is usually enough to filter the light for them). Most thrive if they receive a 'misting' now and then to create a bit of humidity and from a liquid feed (baby bio, etc) during their flowering season.
...and as a rough guide, ferns like bathrooms, dracenas or tobacco plants like darker areas, peace lily's like electricity (ie. next to the pc - I kid you not!) calatheas also like a slightly shadier area. Aloes and spider plants are happy virtually anywhere, as are trandescanthias, but jasmines like quite bright light.
Go for whatever you like the look of and move it around until it looks happy - that's what I tend to do!