JIRA is a very extensible bug/task tracking tool. As such, newcomers feel lost as to what plugins they should install.
Please share your thoughts what plugins (both free and paid) that you consider a "must-add" for JIRA!
Here are the plugins I couldn't live without:
Timesheet report - Summarizes any user's time spent over a weekly period: http://confluence.atlassian.com/display/JIRAEXT/Timesheet+report+and+portlet
Charting plugin - Generate charts from any issue navigator: http://confluence.atlassian.com/display/JIRAEXT/JIRA+Charting+Plugin
Subversion plugin - Link and view subversion commit history to a JIRA issue: http://confluence.atlassian.com/display/JIRAEXT/JIRA+Subversion+plugin
Labels plugin - Lets you tag any JIRA issue and search on tags: http://confluence.atlassian.com/display/JIRAEXT/JIRA+Labels+Plugin