Another place to get supplies online is:
http://www.uline.com/I reuse boxes as much as possible, as well as quality packing materials -- foam, bubble wrap, etc., but when I need special size boxes, more beefy packing materials, extra wide bubble wrap, etc. there is a real great shipping supply company not too far from my home, and I can get just about anything I need there.
Thepink insulation foam from home depot, as well as the thicker "cooler foam" that others have mentioned, is also very useful for large, heavy items.
I've sent turntables, large, heavy speakers and tube amps, and just about everything else audio related you can think of, and aside from one pair of speakers, neverhad a problem (but I don't use UPS).
You can bet that when I'm finished restoring my vintage JBL L-300 Summits, my Marantz 4400, and my Akai GX-747D open reel decks, that they will get custom made hard crates for them. The business next door to the shipping supply house I use, does high quality crating (they made the crates for the Hubbel telescope mirrors), and they're pretty reasonable -- approx $225 for a custom crate for the pair of JBLs, with a final weight of about 500 pounds.
Their is a national chain called "craters and freighters" -- they are outrageously expensive, and refuse to insure anything unless they wrap their solid gold crates around it.
HTH
-- Jim