Pretty much anything but a bread knife (serrated, with a round-tip) will find its way into a target, 'round here!
In fact, it's not unusual for me to buy two of a knife that I like the shape or heft of (one for the wife and the kitchen, another for me to throw without getting in trouble).
Pocketknives throw well, but generally won't last since they're either built to really exact tolerances or not built to take the stress.
Khukris throw satisfyingly (much like a 'Hawk), if you can find the spin.
I'm trying to grab a couple of cheap(-ish), full-tang swords to try throwing.
Another "non-throwing knife," I'm tinkering with are the 18" segments of rebar you can get for projects from Home Depot. We have about 20 of them laying about, cluttering up the garage. A few minutes on the grinder, and they vaguely resemble ballista bolts. Heavy, pointy, and from the look of it, downright nasty!
Other than these toys, pretty much any heavy fixed blade will work, although "camp knives" seem built especially ruggedly for it.
Have fun!!
