Bug/Issue tracker for Drupal 7?
Solution 1: Do It Yourself

Add taxonomy terms 


Status (Open, In Progress, Pending, Resolved, Closed) ,     
Priority
(Low, Normal, High)


Create content type Issue, 


add fields title, body, status, priority.


Set roles


Allow anonymous users to create content Issue
Allow administrators to edit and delete content Issue


Extras:

Use Views for issue reporting 

Use Workbench for managing issues 

Use Workflow for setting issue management workflow 

Solution 2: Use an external issue management solution 

Comparison of issue-tracking systems 

I prefer an external solution because of its independency I can still handle issues even if my site is down.