I've been using the MYN system [1] for the last couple of years for work-related todos. One aspect of it is what you could call a "priority stack". That is, it behaves like a stack, except when you reprioritize items by pulling them towards the top of the stack (upon daily/weekly/monthly review). Items that turn out to be not important/urgent will tend to sink towards the bottom of the stack, and the further down the stack, the less frequently you review them. The algorithm is based on the insight that (a) you can't possibly get everything done that you capture as a todo item, and (b) you don't know beforehand which items are the ones that you can (or will have to) discard. The staggered review process however automatically sorts them out.
Like GTD, MYN is a commercial product, however the book is affordable and the main chapters are well worth reading, even if you don't use Outlook or Toodledo (the two main tools used to present MYN).