Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Collabtive - Collabtive is a web-based project management software.
Planyway - Visual project management for Jira and Trello: manage resources, build project roadmaps, use time tracking.
Teamwork - The Project Management App for Professionals. The most powerful and simple way to collaborate with your team.
Corrello - Dashboards for agile teams using Trello
Flyspray - The bug killer!