Billing Tool/CPQ recommendation for subscription/usage-based model needed

We just implemented Ordway (www.ordwaylabs.com). We have a very complex pricing structure and very few solutions in the market could handle it. There are levels of billing automation you can set, too, so that you can get comfortable with the system before setting it on "auto". Once you do, it automatically handles the entire end-to-end process from initial order to customer management including renewals (both manual and auto), to invoicing and payments (with configurable email workflows for past due invoices and dunning), to revenue recognition. It is a very flexible system and I would recommend it. They have a lightweight CPQ system, but I've seen improvements to it lately and they mentioned that it will be a focus in the coming months.