In the event that you are puttering through mhartl's fantastic RailsTutorial as I am and had the same "a ha" moment in Chapter 11 where you need to set up an Amazon S3 account to host your production environment's image uploads, I offer this quick gist (forked from derrek). The "a ha" moment?
Wondering if you can just use DreamObjects instead of S3, since you already use Dreamhost.
You'll be doing some changes with RailsTutorial's Listing 11.65, but it will stay mostly the same given the compatibility with the S3 API.
In the DreamObjects web GUI, if you don't already have a bucket, click "create bucket". Name the bucket. For this example the bucket is named testing-bucket. Click the link to "Change Settings" for the bucket and then toggle the "private" switch to "public".