Synthesizer newbie help?

[Blunderland]

I recently posted after trying to create the 555 oscillator circuit available at the following website:

http://www.scottmetoyer.com/archives/simple-555-synth

I originally was having problems but have now managed to successfully create this circuit.

I now wish to extend this to make a more complex synthesizer or at least one with more oscillators.

The oscillator I've created is a square wave. Can anybody recommend any simple schematics to create another kind of oscillator (e.g. sine, triangle, e.t.c). Or any other simple schematic to extend the synth (e.g. low pass filter).

Also how would I then integrate the other schematics into the one I've already built? How would I send the outputs to the same output of the 555 timer oscillator would I just plug into the same line on the breadboard? Also would I be able to use the same battery or would I need more power?

I'm really trying to keep this as simple as possible as I'm brand new to electronics. I set myself the task of building myself a synthesizer for a University project and I think I was a little advantageous before I realized it was a going to be quite so complex. I only have about three weeks to complete the project so as simple as possible if that is possible....

Any help would be hugely appreciated!