Homebrew sans the flash cart [Update]
A site called Winsunx is getting ready to release a device suitably named the "Ninjapass". As opposed to previous flash cart setups, this wonderous piece of hardware is quite literally a DS cartridge, functioning normally and independently in your regular DS slot. It comes with a USB 2.0 adapter for easy access to your computer, a convenient way to save game files (previously quite troublesome), and a multi-game menu built right in. It's currently slated as a pricey $51.99, but that may be a bargain for the kinds of illicit pleasures that may come.
[Thanks, Mike Lacks!]
[Update: Fixed a typo. Good eye Mike!]