Although there already exist many websites about such stuff, another simple DC-DC converter is described here. The output voltage equals twice the input voltage minus the voltage drop across the diodes.
http://df2ck.de/tech/dcdc/
http://www.uoguelph.ca/~antoon/circ/car912.htm
http://www.aaroncake.net/circuits/6-12conv.htm
simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input, extremely useful for powering opamp and other circuits that require a dual voltage from a single battery
http://www.aaroncake.net/circuits/vinvertr2.htm
Simple circuit that will quadruple +12V input.
http://idt.net/~ljg19/cpump.pdf
http://www.interq.or.jp/japan/se-inoue/e_ckt27.htm
This circuit will generate a smaller DC output voltage from a larger DC input voltage.It is quick and simple to make and by changing the value of the zener diode, the circuit can be universally adapted to provide other output voltages. The circuit and all
http://www.mitedu.freeserve.co.uk/Circuits/Power/dcdc_con.htm
http://www.web-ee.com/Schematics/5%20to%2015VDC/5_2_15.htm