I just created my first project on blimp and I really like it. It seems to be very easy to use and has almost every feature I need. You could add a messaging feature for the users that are involved in the project.
Just one feed with the face the time and the message for discussing new ideas.
I will definitely recommend it. Good luck with it.
I'd like to second this suggestion. The app seems very intuitive and pain-free to use, but in past projects I've found teams often rely heavily on Basecamp's messages for keeping track of ideas and debating/hashing out features, and it's important to be able to track those discussions with the rest of the project data.