The 555 timer is a generic chip that's now made by various manufacturers; you can read about its history and more on the excellent Wikipedia page.
For the video-inclined, here's my Virtual Workshop with these projects:
UPDATE: 123D Circuits adapted my awful synth into a version you can play in your browser! Check it out here, or just scroll to the bottom of this article to play it!
I also recommend this fantastic resource for learning about the 555; it has a bajillion example circuits, plus all the basic intro material right up top: http://www.555-timer-circuits.com/
"Flashing LED with 555 chip" – Kit 1, Circuit 11
This basic circuit blinks an LED at a certain rate. It's powered by a 9V battery and uses two pretty big capacitors.
"Varying the 555 Timer Pulse" – Kit 2, Circuit 12
This one got me more excited because it's the stepping stone to a chiptunes-tastic square-wave synth! The coolest thing to do after your blinky-LED Hello World. :)
Funnily enough, this is actually a simpler circuit than the previous one. It does require a 4.5V power source; I'm betting that I could get away with a 5V portable USB charger with the leads stripped.
I expect future explorations to take a route through this project:
Atari Punk Bass
This is a version of the Atari Punk Console! I <3 square-wave synths, and like the video shows, I have a whole rail of 555s, so I'd like to build a few weird instruments with these.
I used Jimmie Rodgers' Atari Punk Console kit to build the ATARITAR, but now it's time to get lower-level and add polyphony! Plus, the APC can get a bit... squeaky... but sounds divine on the low pitches.
I'd be combining this with either some conductive material (like PLA) or a linear soft potentiometer... Annnyway, I'm clearly going down a rabbithole, so it's time to wrap up this write-up. :) Tell me what you wanna make!
...maybe I'll throw in a wah-wah...