I would like to suggest a new feature that affects the products and quotes modules.
It would be nice you could define two tipes of items lines costs. One for one time prices (as it does work now) and a distinct type for periodical cost services (rents, montly services, etc…)
This way, when you build a quote, you can specify in a separate way what costs are one time, and what costs are, for example, monthly.
I havent been able to figure a way to do it with actual functionality.