I heard some sort of knocking coming from my front end. Upon further investigation, the LH front wheel was loose (all of the lug nuts were tight. When I took off the wheel, there was noticeable movement on the rotor (1-2 mm) with my hand. My thinking was a bad wheel bearing, but a friend suggested ball joint. How can I tell?

 

Sounds like a "Wheel Bearing" if the lugs are tight and you could still wiggle it. Maybe take it to an axle repair shop... should be pretty easy for them to fix.
Good Luck

 

Yeah I also agree that it sounds like a wheel bearing. My coworker has a 95 Accord and the exact same thing happened to him. When off the ground with the wheel on and fully tight you could still shake the wheel like it was loose.