What PM programs that have you used that are free or at least cheaply priced that works well for 5-10 people?

I have a handful of clients who are all looking for a PM software to start working with now that they are getting more established but do not have interest in putting a lot of $ into it up front.

I've researched many of them and read articles but I'd love some insight from more people who have hands on experience and can give some feedback.

Thanks!