Favorite prototyping and product materials online sources?

What stores does everyone use to buy prototyping and/or product materials online? I’ve been having a hard time finding companies online that will let me order smaller order sizes of some materials. Bonus points if the price is great and I can order samples too. I live in the midwest (US) if that makes a difference.

The materials I’m most interested in are:

  • thermoplastic sheets for vacuum forming
    CNCable rigid foam
    pink/blue insulation foam sheets (XPS) for prototyping
    liquid polymers for Jesmonite/other polymer-modified plaster casting mediums
    white artisan concrete
    colorful concrete aggregates
    concrete colors
    acrylic sheets for laser cutting

I was able to find a local plastic supply warehouse (through lots of googling) and found they have scraps and things, but it is unpredictable and they don’t do online biz. In my experiences a lot of places like that are pretty old school. Also, the local Dick Block had a fire sale on balsa foam, not sure why. I find going to the local shops you can usually get the deals. Same with foam core. Took me forever to find a place that would sell a few sheets of 4x8 foam core and not charge an arm and a leg, but finally found a local sign shop that was wiling.

Hoping someone has some better answers though!

McMaster Carr
Dick Blick
Freeman Supply
Speedy Metals