Apart from the list of Kanban tools at Tools Journal, there is another list at the Limited WIP Society website and another one at Agile Scout.
(Unfortunately, as a new user I can't link to each one individually. Here is a link to all the lists)
You mention in your question that you want a Scrum board. This is different from a Kanban board. (Most of the other answers seem to be about Kanban boards, so it would help if you could clarify on that)
As you can see there are many tools out there. Which one you choose depends on what you need from the tool.
If you just want something to track your personal work then a solution like Simple Kanban is easy to get started. One step above are really simple tools like Scrumy and SeeNowDo. They are both free and give basic scrum board capabilities. (Sorry, I dont have the rep to add links to them yet.. perhaps someone can edit this answer with links?)
If you want to collaborate with others, and use it in a software development team (possibly distributed) then you will want a more powerful tool. More powerful tools include support for creating complex boards, metrics, reports, commenting, APIs, and so on.
So you need to tell us more about your needs before I can make a recommendation, as there are different tools for different use cases.
The company I work for develops an agile tool suite at http://toolsforagile.com It is a set of team level boards, and support both Scrum boards and Kanban boards, with all those features I mentioned above like metrics, API, etc. It is geared towards team collaboration, but there is a free starter plan for 1 user if you want to check it out.