We just showed you ThinkGeek's Pocket Retro Game Emulator, which was barely a week old. Today, the site is neck-deep in orders for the unit, and it's easy to understand why. ROM-enabled portables such as the PRGE are a siren call to anyone who has a sizable ROM collection, or is looking to start one.
In case you need a refresher, the Pocket Retro Game Emulator can play both 8-bit and 16-bit games from NES, SNES, GBA, Sega Genesis, or Neo Geo ROMs, and features 4GB of built-in storage (as well as a micro SD slot in case you need more than that). It really is pocket-sized, with a form factor about as large as Nintendo's Game Boy Micro. That also means a small screen to play on, if that bothers you.
At $100, you get the unit, power adapter, USB cable and a set of earbuds. ThinkGeek is looking to stock up on more soon.