Lately we've been using Pivotal Tracker to manage tasks in our team. I have to say for a team of 5-10 people the product works great as a task tracking tool. The only drawback is that the number of states a particular story/task can be is limited. But for a small team like ours with a straightforward workflow it is usually not a problem. A story/task can be in one of 5 states -
1. Not Started
2. Working on it
3. Finished but not yet delivered
4. Delivered and waiting for acceptance/rejection
Pivotal tracker is not free and the basic plan starts from $7/month.
I'm also trying out Trello which is a free Kanban Board. This type of task/story management is useful if you are dealing with processes which usually follow a certain flow and can be categorized in to distinct buckets.
Another tool for Kanban Boards is Kanbanery. According to the website you can create a free account. I'd like to try this sometime.