I can recommend you this FREE extension.
It kind of does what you need, but it requires some configuration in the backend.
The extension allows you to create lists of products (with filters and all) based on some rules.
The rules are similar to the discount rules that come out of the box.
In your case, you can create for each brand you have a rule, that looks like
brand is ... brand name here.
The only downside is that each time you add a new value for brands or remove one you have to adjust the product list rules.
The upside is that each time you set a specific brand to a product, the product will appear in the list automatically.
Even if this does not fully fit your needs, you can use the code as an example and adjust it to what you need.
Documentation can be found here.
Note: I am the developer of this extension, but I get no financial benefits out of it.