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.
Toby - Better Than Bookmarks
Planyway - Visual project management for Jira and Trello: manage resources, build project roadmaps, use time tracking.
Workona - A better way to work in the browser.
Corrello - Dashboards for agile teams using Trello
Tabbie - The missing tab manager for Chrome