The hydrides of boron are the exact opposite of boring. Weird-ass structures, electron-deficient bonding, and so on.
The element also forms some very hard ceramic materials, and colors flame green.
I agree completely about phosphorus, though. Amazing stuff.
Silicon is either incredibly boring or the exact opposite, depending on what it's bonded to. It's also incredibly common. The fun (and dangerous) forms almost always revert, with vigor, to the boring forms. Case in point: Silane, SiH4, the silicon version of methane. Nothing like it (except it's also a gas) - probably a lot more toxic, and bursts into flame spontaneously, producing extra-fine particles of glass if you let some of it escape into the air, which must be great for your lungs if you're exposed to them. (Though you can do small demonstrations that are roughly harmless. I think you can reduce glass to magnesium silicide with magnesium, then react the chunks of Mg2Si with water.)
Silicon tetrachloride is easily attacked by water, also making glass. I bet you could have a lot of fun pouring the stuff into water.
Carbon may well be my favorite. I've heard it said that carbon is special because it isn't - its bonds are just unreactive enough that you can build stable structures out of tens, hundreds, or thousands of C atoms. Its tetravalency and ~400 kJ/mol (maybe less? can't remember) C-C bond are what makes it king.
Least favorite? Actinides, because most of them are just of theoretical interest. And they're too radioactive for me to go anywhere near in real life. =P
The science flew off Gordon Freeman's face and landed and blowed up in a BOOM!