I made some wordlists a while ago containing common usernames. They have proven very useful to me when doing application penetration testing, specifically they are great to use as the payload for Burp Intruder.
I created the lists by taking the 10,000 most common last names in the United States and prepending a single letter (for example "dferguson" appears in the usernames-d.txt wordlist). There are wordlists for all letters except "i", "q", "x", and "z" (frankly, there aren't many first names that begin with those letters so it's a waste of time to try them).
Click here to get the username wordlists (zip)
One scenario where you might leverage these wordlists is a web application where the login page returns a different error message depending if a valid username is received versus and invalid username. Run Intruder on the login request and you can probably reap a nice set of valid accounts.
You'll also find a special wordlist called usernames-top100-each-letter.txt. This is perfect when you have limited time and want to maximize your potential to find a valid account. And there's another list called usernames-generic.txt, which could help you discover some test accounts. Of course you can combine these wordlists any way you want (even concatenate them together and try the whole darn thing).
Things get a little more complex if the web app requires an email address for login. You could certainly append "@gmail.com", "@yahoo.com", "@aol.com", etc. to the usernames. Separate wordlists could be created for each email domain, or you could just leverage the power of Burp Intruder to append the domain on the fly.
