Asana is next to Basecamp, but many users say that they prefer Asana more because of its simplicity. Aside from that, Asana is free for 15 members for unlimited projects. I have created an account and already trying it out. Personally, I can say that Asana specializes in task management. Yes, it is very simple and intuitive but lacks on many aspects.
RallyDev is the most popular when it comes to Agile Project Management. I have already signed up and been exploring the demo. Its Community Edition is free for up to 10 users and 5 projects. What I like about Rally is it has many features. It is really Agile. You can create User Stories, Backlogs, set Estimations, track iteration/team/product status, facilitate test cases and lot more. The learning curve might be steep, though. I am still trying to figure out how the Product Owner can create User Stories.
The Visual Studio’s TFS can also do Agile management. But, I am not sure if this is restricted only to the team (within the company) or if we can give access to the users (and if it is advisable). I have to dig deeper about that yet.
There is Trello, Insightly, Flow, Jira, VersionOne etc but I think it all boils down to what the team really needs. And since, we are starting up, maybe we can utilize the free one(s).
As for UX tool, I am hearing about Balsamiq a lot. There is no free version, though. Just trial versions. I might look at InVision. It looks promising.