Ask HN: extendable project management tool for a 20-50 people Internet company?

I have been searching so many project management tools such as Redmine, JIRA....etc. There are pros and cons for those software. The redmine seems not so user friendly for a beginner although I think it's worthwhile to get used to it. The JIRA is more beautiful but isn't free. I'm not quite sure whether it's extendable or not. The teambox and trello is beautiful and easy to use, but it seems that they are not good for the size of my company both. Are there any other goods or view of points?