RESTful POSTS, do you POST objects to the singular or plural Uri?

In RESTful design, there are a few patterns around creating new resources. The pattern that you choose largely depends on who is responsible for choosing the URL for the newly created resource.

If the client is responsible for choosing the URL, then the client should PUT to the URL for the resource. In contrast, if the server is responsible for the URL for the resource then the client should POST to a "factory" resource. Typically the factory resource is the parent resource of the resource being created and is usually a collection which is pluralized.

So, in your case I would recommend using /products

Since POST is an "append" operation, it might be more Englishy to POST to /products, as you'd be appending a new product to the existing list of products.

As long as you've standardized on something within your API, I think that's good enough.

Since REST APIs should be hypertext-driven, the URI is relatively inconsequential anyway. Clients should be pulling URIs from returned documents and using those in subsequent requests; typically applications and people aren't going to need to guess or visually interpret URIs, since the application will be explicitly instructing clients what resources and URIs are available.

Typically you use POST to create a resource when you don't know the identifier of the resource in advance, and PUT when you do. So you'd POST to /products, or PUT to /products/{new-id}.

With both of these you'll return 201 Created, and with the POST additionally return a Location header containing the URL of the newly created resource (assuming it was successfully created).