I like how Sly Dog Studios makes most of its NES games available as free downloads. The developer puts ROM's of his games as well as demos, screenshots, NSF's, and source code online for anyone to download and use for free. But if you want cartridges, his associates sell those too (RetroUSB, Infinite Lives, et cetera).

To make things easier, he also makes a ZIP file available with all the free NES games included to use with emulators and flash carts.

If you don't know where to start, try his Metroidvania game called "The Mad Wizard: A Candelabra Chronicle."

If you try any of his games, return here and tell us what you think! I'd like to know what's worth playing.