So I'm looking into a proper cloud storage for "collaborato" :) and I've come across a few options (please list any/all others).
Feel free to read the details below, but my initial analysis is to use Amazon since they offer a "Free Tier" which will cost nothing to startup and our bandwidth, storage and file operations will be capped per month.

From an API perspective, REST/SOAP seem to be defacto.  Google provides a JSON API although .NET, Java and Python seem to be standard implementations.  All APIs use similar terminology "DELETE/INSERT/LIST/ETC", and refer to data as "BUCKETS/OBJECTS/ETC" 

Here's the pricing details.  EMCs wasn't readily available.

Pricing:
  • Google
    Storage:  About $.02/GB/Mo (500GB would be $10)
    Bandwidth:
       DOWN:  ~$0.10 - $0.20/GB (Varies based on region) 
       UP:  FREE
    File Operations: $0.01 per 10,000/1,000 (operating depending)

  • Amazon
    Storage: About $.03/GB/Mo  (500GB would be $15)  First 5GB Free using "Free Tier"
    Bandwidth:
       DOWN: ~$0.10/GB First 15GB/Mo Free using "Free Tier"
       UP:  FREE
    File Operations:  $0.005 per 10,000/1,000 (operation depending) First 20,000/2,000 free using "Free Tier"
  • EMC
    (hides its pricing behind an inquiry screen)
APIs:
  • Google
       Java/JSON
  • Amazon
       REST/SOAP
  • EMC
       REST/SOAP
       Claims to also support NFS/CIFS
       
-Tres