A video from Nate McCoy documenting the making of a MIDIBox SID.
The MIDIBox SID is a DIY synthesizer, based off of the MOS Technology SID sound chip, the 8-bit sound source of the Commodore 64 computer.
More information on the MIDIBox SID:

http://www.ucapps.de/
http://forum.midibox.org/
http://www.midibox.org/dokuwiki/
http://www.avishowtech.com/mbhp/buy.html

Demo videos of the MIDIBox SID.

http://youtube.com/watch?v=lnTh4e0b-ic
http://youtube.com/watch?v=FrgdErwTJ5o

Here’s something out of left field:
Shredz64 is a modern day game for the Commodore 64 that makes use of the Playstation guitar controller hooked through the PSX64 interface.
Its design is modeled after the popular “Guitar Hero” series, geared toward the ability to play along to your favorite C64 music on the guitar. Correctly played notes [...]

Odosynth’s 388911 bytes is a freeware/donationware Commodore 64 style virtual synth for Windows. 
Features:

1 oscillator with 4 difftent waveforms: Saw Triangle Pulse and Pitched noise
3 BPM sequencer with 7 rates and 2 to 8 steps .You can end a sequence or loop it.
The first sequencer has notes from c to b and octaves from -3 to [...]

 

  388911 Bytes Demo [1:51m]: Play Now | Play in Popup | Download

The Music of Kraftwerk, by the a group of lo-fi groups collectively known as the 8-Bit Operators, is more fun than any CD we’ve heard in ages.
8-Bit music is a fairly obscure genre of electronica. The 8-Bit operators, though, made a smart move, organizing many of the most influential 8-bit musicians together to create this [...]

Puremagnetik has released Eight Bit, a selection of 1980’s SID chip samples.
Recorded directly from an original 6581 SID chip (as manufactured in the Commodore 64 home computer), the Eight Bit library includes a unique palette of basses, leads and pads. Puremagnetik has captured the sonic qualities of the SID and reprogrammed them into the Ableton [...]

Synth fans: Don’t watch this video of the MIDIbox SID Bassline unless you’re ready to lust after something that can’t be bought:

You can build one, though. The MIDIbox SID, based on the Commodore 64 sound chip, is a very cool DIY project.

What can you do with some worthless old computer equipment when you have too much time on your hands?
This site shows that you can do a lot, if the worthless old computer is a Commodore 64. Back in the days, the Commodore 64 was one of the first personal computers. They were popular before Apple [...]