If you're talking about shipping gallery wraps, you can sometimes get away with a lightweight box if the corners are well protected.
Check these out, which basically tightly couple loads on the corners to the stretcher bars, which may be OK with light packages.http://www.uline.com/BL_2154/Foam-Protectors
The theory is, is you can keep the overall package light enough, gentle underhanded throws and drops at UPS will not result in damage from the weight of the package itself. Art.com and other mass shippers of gallery wraps and small framed pieces take that approach, or something like it using beefed up cardboard corners.
But if your piece has a frame or weighs more than about 10 lbs, better make a simple crate, as discussed in a recent thread here.
When I hand large pieces of art to buyers at shows, I just wrap up about a foot of both ends, usually with the packing foam that comes in boxes of moulding. Kind of puff it up around the corners, then stretch two 17" rubber bands around the foam at each end to secure it.