I use Trello to plan and manage software projects as well as a weekly planner to keep track of my work related tasks.
This is a list of my favourite Google Chrome extensions for Trello which make it easier to use:
Scrum for Trello
Adds functionality to estimate and track story points or hours. I wrote a detailed post on this at Trello.com – Estimating & Tracking Hours.
CardCounter for Trello
Shows the number of cards in each list at the top right of the list.