I'm a big fan of WinCDEmu myself. Acts as an external removable drive. You can mount any number of ISO files without needing to configure drive letters and the like, and ejecting the disc removes the virtual drive and letter. It's also Open Source
Used to use Daemon Tools, but this solution makes more sense to me. Whether it has copy-protection features or not I'm not sure, but it certainly works for everything I need it to do.
Plus there's a beta portable version for those of you who need it.
Really, it boils down to a fast, efficient, zero config solution. I'm fairly certain it runs as a driver of all things, not a straight application.