EDIT: Kanbanize is a commercial product and offers a 30 day free trial.
Disclosing: I am a co-founder of http://kanbanize.com/
Mark, I understand your desire to find the perfect application with all these features inside, but I really doubt that you will get it for free. There's a bunch of super cool apps (including Kanbanize) out there, but none of them is completely free.
Be careful what you call a Kanban board and what not, though. Trello is definitely NOT a kanban system (no WIP limits, no analytics, etc.). It is a great visual management system, but not a Kanban one.
Finally, to answer your question, tools that deserve attention in my opinion are:
Kanbanize (of course), LeanKit, KanbanTool, Kanbanery and probably a few others. My personal bias is that LeanKit is the most advanced to date followed by Kanbanize and KanbanTool.
I hope that helps.
