Rufus

Rufus is an utility that helps format and create bootable USB flash drives, such as USB keys/pendrives, memory sticks, etc.

It can be especially useful for cases where:

you need to create USB installation media from bootable ISOs (Windows, Linux, UEFI, etc.)
you need to work on a system that doesn't have an OS installed
you need to flash a BIOS or other firmware from DOS
you want to run a low-level utility

Despite its small size, Rufus provides everything you need!

Oh, and Rufus is fast. For instance it's about twice as fast as UNetbootin, Universal USB Installer or Windows 7 USB download tool, on the creation of a Windows 7 USB installation drive from an ISO. It is also marginally faster on the creation of Linux bootable USB from ISOs.