Reset your Mac's EFI Extensible Firmware Interface) password

So you're locked out of your mac because a firmware password has been set and you forgot it. Don't worry, there is hope and you have several options:

Firmware Password Utility: 

• Boot from OS X Recovery (Time Machine, USB, internet recovery, etc.) 
• Go to your Utilities Menu and choose Firmware Password Utility to either reset your password or to turn it off. 

Firmware Password Utility

 EFI Reset Tool (I also take no responsibility for any illegal use nor do I condone this). 

• Go here to read about the tool: http://hackaday.com/2013/02/26/mac-efi-pin-lock-brute-force-attack-unsuccessful/. Sometimes this method doesn't work and there is a reason. 

Reset PRAM/NVRAM three times:

• Add or remove a stick of ram. Obviously if you have one stick in, add one and if you have two in remove one. 
• Power on the mac and immediately press and hold command-option-P-R. 
• The system will restart with the ‘bong noise’, allow it to do this 3 times. On the third ‘bong’ you can let go of the keys. 
• The machine will now boot with a cleared password and reset PRAM/NVRAM. 
• You can shut down the machine and replace the original ram configuration. 

Hold in the power button:

• Press the power button for ten seconds until the front indicator flashes. 
• Keep holding the button till the mac starts up; this way your Mac EFI is reset. This will help in a lot of problems. 

If nothing works, I am afraid you will need to go to the Apple store and show proof of purchase before they reset the EFI for free. Here is a little more information on this topic.

Lion doesn't come on any physical media.  Instead, you have download it from Apple's servers from the Apple store.  What if you bought a Mac with Lion already installed and you desperately need the install DVD because your hard drive got hosed.  The following will give you instructions on how to burn your own install DVD.

1. Download Lion from the Mac App Store. The installer should show up in your Applications folder.
2. Right-click on the installer and hit "Show Package Contents". Navigate to Contents > SharedSupport and look for a file called "InstallESD.dmg".
3. Open up Disk Utility and drag the DMG file into the left-hand sidebar. If you're burning it to a DVD, insert your DVD, select the disk image in the sidebar, and hit the "Burn" button. Skip down to the last step to use it.
4. If you want to burn Lion to a USB flash drive, plug it in and click on it in the left-hand sidebar in Disk Utility. Go to the Partition tab and select "1 Partition" from the dropdown menu. Choose "Mac OS Extended (Journaled) on the left.
5. Hit the Options button under the partition table and choose "GUID Partition Table". You'll need this to make the drive bootable on a Mac. Hit the Apply button when you're done to format your drive (note: it will erase everything on the drive).
6. Click on the "Restore" tab, choose the InstallESD.dmg file as the source and your flash drive as the destination. Hit the Apply button and it will create your bootable USB drive.
7. Reboot into OS X and hold the option key when you hear the startup chime. You can boot into your DVD or flash drive from there.