Kanban is a process where you divide your work into stories, and place them on a visual board. You pull stories across the board into different columns as the story progresses. Typical columns are "ready to pull" (first column, this story is ready to begin work), "in progress", "in test", "complete". The idea is to focus on getting cards across the entire board, and having few cards in flight at a time. This is generally believed to increase productivity by avoiding the urge to multitask too much. It can also reveal bottlenecks in your team's process and generally is good at visualizing how your team gets things done. Which can be eye opening.
Since I'm all by myself, my kanban board is really just a fancy todo list. I am using http://www.agilezen.com for my board. Trello is a more well known app along these lines, but purists disagree that Trello truly accomplishes Kanban because it's missing a few key Kanban concepts (whether that really matters is up for debate).
Have a look over at JoelOnSoftware (?? Or was it the Fog Creek Site?)
They have a free online version of something similar that they are trying to hit the big time with. I forget what it is called though.
Here is the Wikipedia article talking about Kanban as an agile process: http://en.wikipedia.org/wiki/Kanban_(development)