Belt driven compressor (oil filled) will be the quietest.
I have one of these I picked up new at Sears for $450 plus tax. Much much quieter than an oil free compressor.
For continuous duty larger tools, you'll need something with much more CFM. I'm no expert, but 10-15 CFM is probably necessary for larger standard size sanders or polishers.
Link included now:
http://www.northerntool.com/shop/tools/product_200375221_200375221