Imagine the box being thrown down a flight of stairs. That will give you an idea of how to approach packing things. I've gotten two sets of speakers from people so far that were merely padded with some bubble wrap. Those thin layers of air bubbles aren't going to protect anything when a box of heavy speakers slams hard into the wall after being flung down one of those roller ramps. There's a reason manufacturers use molded styrofoam to ship their gear and not bubble wrap. Needless to say, in each case the speakers were cracked and damaged to various degrees, one to the point where it had to be returned for insurance, etc.
If you do use bubble wrap, use it as only one part of a more complete packing job. Wrapping the item itself in bubble wrap is fine, but make sure you also have real physical protection, like styrofoam, peanuts, the various kinds of paper padding, etc., not just a thin sheet of air bubbles that you could literally pop with your fingers. That's not going to protect heavy gear from getting slammed around like these shipping places do. Double box everything with a buffer layer of padding in between, and for extra protection wrapping the item in plastic like analog2digital said is also a great idea to protect against possible water damage.
Stop at local businesses or maybe even wal-mart to find boxes and packing materials that they are getting rid of. Sometimes you can see piles of them in back of a store that no one is going to mind if you take. Depending on the place, it might be a good idea to ask someone first, just to be sure. But most places won't mind. As long as you're not burning tanks of gas driving around to find empty boxes, it'll probably be cheaper than paying fed-ex/ups to pack it for you.
