Planning Projects portfolios

Can anyone provide me with examples of strategies they have employed to plan and prioritise projects.

I personally like the thought of having a pipeline of "things to do", change requests, defects, new features etc.. which are added to a backlog and prioritised by Product Owner(s)...but how can this work at a say corporate level, can a Giant SCRUM work which feeds into multiple teams that pick the "things to do" from the prioritised list work? We like most companies are constrained by resource so I see a kanban style as a possible way to feed the development teams, but not sure how this would work in practice, anyone shed any light on how they have done this.