Decent eBay items.

Taken from Ebay.

The INVERSEROOM PHOTOSYNTH is a one-oscillator miniature synthesizer that outputs a simple square wave, which the user can change with a variety of control and modulation options. Only five inches long, the PHOTOSYNTH incorporates a phototheremin, LFO, depth control, and eight modification buttons to create a huge range of bizarre electronic bleeps, blips, whoops, and squeals. It’s ideal for experimental, glitch, electronic, and noise music, and runs on a single 9-volt battery. The PHOTOSYNTH is based on two IC’s, a 4049 inverter, which produces and amplifies the signal, and a 4049 binary counter and resistor array, which control the LFO. Pitch can be altered with a potentiometer through a range of more than ten octaves, or by a photoresistor, which allows the user to play the instrument like a theremin. This sensor is activated by engaging the SEN switch, and allows the user to control pitch according to the amount of light that reaches the PHOTOSYNTH. The MODIFY panel of buttons can then effect a series of short-circuits that change the synth’s sound in unexpected ways. Some may seem to have no effect at all at some pitches, and drastic effects at others; some alter the output waveform, speed up or slow down the LFO, or create bursts of sudden noise. Below are two mp3 sound samples, one illustrating the sound of a steady pitch being altered by the MODIFY panel, the other with the LFO engaged. Sample #1

Sample #2 The PHOTOSYNTH also features a combination ON/VOL knob, and an LFO DEPTH knob. Output is through a standard quarter-inch phone jack. The instrument is hand-built, wired point-to-point, and contained in a sturdy aluminum case standing on wide rubber feet. The 9-volt battery is easily changed, and a new one comes included in this auction; I will also include an instruction sheet.

When I first saw this I was like damn, thats pretty cool. How would one go about building a synth like that. Well after searching through the seller's past auctions. I found my answer.

A simple investment into a kit.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=11737&item=5976166013

You are bidding on this Smart Kit #1045 Sound Effects Generator. An easy to build project that will create many interesting sound effects. It can produce many different sounds from bird chirps to sirens. The circuit can be operated from a small 9V battery. Supply voltage: 9 VDC. Max. Current: 200mA. Output power: 0.05 Watt.
And for 12.95 one has all the necessary info to build such a device. It sold for $95 dollars without a problem and I would imagine that there will be more avaliable soon.
The counter and devider ICs used are totally interesting because typically a simple analog oscillator is what most circuits use.

Another product from the seller that has cought my attention is the Altoids theremin synth.
They bought some empty cans and the synth chips.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=38071&item=7323096180#ebayphotohosting
There is alot of info on the auction site, however from what I can gather, its better then 555, Its a linear VCO with Triangle and Square. The sweeps are also possible on the chip( 1000:1).
The chips a rare I guess, but copied versions are avaliable under these part numbers.

National Semiconductor copied this part under the P/N LM566 LM566C,
and NTE Electronics, Inc. copied this part under their own P/N NTE994.

SIGNETICS was the original manufacturer and produced a better part.