I'm new, but I found something that might help a few people who play without a shoulder rest .  

I recently got my first student violin, and it came with the standard cheap shoulder rest.  I didn't like it at first, as the violin hurt my jaw a bit.  I later discovered it was the chin rest and made adjustments, but before that, I set off in search of something to pad my shoulder a bit.  The sponge method seemed not to work well for me, and didn't really help with the slipping.  I was at Walmart when I discovered a silicone trivet, a pot holder.  It's thin, will conform to my shoulder, doesn't slip, cheap, and because of the honeycomb style texture, still provides great padding for my bones.  Here's a link, though you can only buy them in the store and mine was black, not the yellow in the picture:  http://www.walmart.com/ip/Gour.....t/22374192