I am working on a web startup in the early stages, and we are struggling a bit to manage the scope and scheduling of our product. We have loads of high-level features in the pipeline, but we need a good way of scheduling them for release iterations and breaking them into actual tasks that can be scheduled (that could be a separate tool, but integration would be preferred).

I would say that our product can be pretty cleanly divided into "aspects", and we want to be able to separate features by the aspect to which they apply. Perhaps most importantly, it should be really simple to create and move features between target release points. We don't have physical space for a war room type setup, so whatever we settle upon should ideally have a cloud-type web interface.

Right now, we're using Excel to make a grid of product aspects vs. target releases, and we store features at the intersections. But this is not providing a good way of indexing tasks to those features or being able to move them around. I would much rather have something that automates the grid overview.

I'm less interested in something that helps with low-level scheduling than I am in something that is good at organizing the product plan at the long-term, high-level view.

Is there a product planning tool out there that matches these specifications?