Agile (and especially Scrum) is very hyped in the software industry at the moment. And I think it is because of the hype that one of the most common questions I hear from people that want to start being agile is "what tools are there to help me?". First of all I think many tool seekers forget to ask them self why they want a tool. Because most teams don't need fancy tools. Actually teams not using fancy tools tend to perform better in my experience. Teams with fancy tools tend to spend a lot of time updating stuff in their tool and less time communicating. I guess that is why the agile manifesto says "Individuals and interactions over processes and tools".
This does not mean we should avoid tools. Sometimes tools are helpful and even necessary to a team. Personally I recommend each team I've worked with to try low-tech tools like post-its and white-board at least one iteration before sticking to a tool. Most teams tend to stick with the low-tech... But if you want to try different tools out then Mike Cohn has compiled a list of tools to help you out.