Since the heady days of the original NESticle emulator for DOS, video game fans have been hacking games such as Super Mario Bros. and Mega Man 2 to change level layouts and alter graphics.  What began as crude and tasteless shock value hacks (naked Mario, racist Mario, etc.) eventually grew into worthwhile creations that turn familiar classics into entirely new games.  John Harris has written a new e-book, Somebody Set Us Up The ROM, that chronicles some of the best hacks that the Internet has to offer.  Part One focuses mainly on games from the worlds of Super Mario and Metroid, while the upcoming Part Two aims at Sonic the Hedgehog and Mega Man.  It's available exclusively in the Summer Smash Game Bundle.  Here's a note from the curator, Simon Carless:

Some people think, with some justification, that romhacks are mostly about seeing how many dongs someone can fit into a single game. But the best ones are far from that. Sometimes they add major features to beloved games to make them playable for a new generation. Sometimes they greatly improve game graphics, or present new worlds to explore. Sometimes they correct terrible design decisions. And sometimes they translate game into other languages, allowing them to be read and appreciated by new audiences.

This book is a collection of good romhacks, small and large, simple and incredible. And without a single dong to be found.

I had the opportunity to read a pre-release copy of this book and I am impressed by the depth of exploration.  Harris dives into interesting ideas such as adding a day/night cycle to Super Mario Bros. 3, integrating an auto-mapping system into the original Metroid, changing the villagers in Castlevania II: Simon's Quest into truthful helpers instead of lying bastards, and so much more.  This is an interesting read that will give you plenty of new twists on old favorites to try.  I eagerly await Part Two.